OTS is more of a catch-all term for multiple symptoms, isn't it? It's kind of like an athletic trainer saying, "tendonitis" because they don't know what the true source of the problem is. I coached a kid about 15years ago who had basically hammered and raced non-stop for 2 years without any kind of break. He was a 16:00 5K high school kid, so not bad. But he got to where he felt achy and tired all the time because every day was like 6:15pace or faster. And he was trying to hit like 60miles a week. Then racing and hard stuff on top of that. I told him he needed like 10-14days off and eat ice cream, drink Pepsi, gorge on his favorite junk food (I know it sounds like bad advice but his body just needed calories and the mental break from not having to focus on training all the time) and then take 3-4 weeks to ease back into training where no day would be faster than 8:00pace for a while. He cussed me a blue streak and his mother told me later he hated me the entire 10days. However, she worked with racehorses and told him the same thing: you've got to give the body a break, even regular breaks, at some point. Or, it's going to shut you down via OTS or CFS. Long story short, he listened and won state championships about 4months later.
That aside, I empathize with you. I have also had this happen to me when I trained in college. I went from like 40miles per week avg in high school to like 75+ a week my first year. I suffered that entire year in college running. Barely raced faster than in high school, even though sometimes my workouts were nearly as fast as high school races! I just didn't give my body time to GRADUALLY adjust to volume and intensity. Came down with upper respiratory infections, low iron, you name it. It wasn't that I was completely gassed all the time. I could finish workouts, and hit the miles, etc., but it was like my body just refused to let me go to the next level. Plus, all my easy days were too fast. Diet wasn't the best and I slept okay, but all the little factors add up over time. Kids that I have helped over the last 10-15 years ask me if there's one thing I could change about my training from years ago, what would it be. I tell them, "I'd slow my easy days down like 45 to 60sec a mile, and I'd cut runs short from time to time if I wasn't feeling it." They all think it's "I'd run harder, or do more volume, or race more." Um, no? And I usually add, "I would have changed my diet to actually FUEL myself better so my body had tools to recover."
My humble armchair suggestion based off your volume and training loads, and I freely admit that I am not a medical doctor or homeopathic/naturopathic doctor in stating this, is that when you feel you are able (or are given a green light by medical people you work with/trust) to start training at a similar level again, that you base your training on RECOVERY type principles more than VO2, threshold, CV, LT, whatever, etc. Don't get so bogged down in exact science and that you have to be doing 'x' miles/workouts at 'y' levels, to achieve success or gains. The body only adapts in the recovery from those workouts. So, making sure your easy days are easy, that you take planned breaks every 7, 10, 14 days, etc., is priority. I also recommend that you really watch what you are putting in your body. As a distance runner/endurance athlete, despite all the popular diets saying otherwise, you need lots of calories from branch-chain carbohydrates that come from whole-grain sources. And this should be from the moment you wake up to the time yo go to bed. (Experiment a little to find out what works best). And lots of protein/iron on top of that (from dark green, leafy vegetables as well), especially in the couple of hours following a hard workout/long run. I've seen kids (upper teens) explode to new levels sometimes just by changing their diets a bit and getting them to eat well AFTER hard runs, races, etc., and understanding basic nutrition and fueling.
I'm not criticizing you nor trying to solve your problem per se. If you feel something is wrong, you've done the first smart thing in backing away and paying attention to the signs. I didn't. It's one of the reasons I trained myself into the ground time after time. OTS usually resolves itself in a few weeks to couple of months by reductions in volume and recovery (as one poster mentioned, making sure you are sleeping well, probably 9-10 hours a day based on the volume you listed)...but also making diet changes. I'd also try to find a local dietician or nutritionist who has experience working with endurance athletes, triathletes, marathoners, swimmers, etc. They are often overlooked by most runners. And maybe find a good physical therapist who can help you devise a basic x-training routine that you do 20-25minutes every 4-5 days. I have found that doing PT type exercises for short 'injury-prevention' sessions works as well as most modern 'strength training'. If you up your volume a lot without some basic yoga/band/plyometric/PT type work on the side, you are robbing yourself of the tools you need to handle that volume. I'm not saying (because I know LRC message board experts will disagree) that strength training will make you faster, necessarily. I am saying that a little here and there HELPS your body handle the biomechanical pounding of running that kind of volume.
If you've already been trying all these things, then I hope you isolate the main culprit get it figured out, and I hope those in your support community (family, friends, medical, etc.) can help you as well. Wish you the best. Train smarter, not harder I have always said to people, after learning from my own mistakes. And even if you have to take some time off (I know runners hate taking time off), you may find you come back better after the break.