Indeed, young women can get pregnant that quickly. Its human biology.
We don't know whether Gidey is pregnant or not, but its certainly not impossible in the way you think it is!
I think its quite concerning that she is no longer competing so after getting married unless she is pregnant or injured. These Olympics are occurring when she is at her physical peak and she has the right to earn a living. Theres quite a history of athletes being controlled by their husbands and one was even murdered by hers, and the split from her coach and management team disconnect are also worrying. She would hardly be the first woman to marry a controlling man who resented her having an independent life and who thought all her time should be devoted to cooking and cleaning for him. I hope she is all right, particularly if she is isolated from her family.