@Awesomekidsmom you asked for advice, so I hope this doesn’t sound overly critical.
You said your son had a skin issue a month ago on his feet, and was prescribed / given something that helped at first, but now it seems much worse. I think it is possible that @TurnerT is correct, but I would recommend an additional Dr visit. It is also possible that if he was wearing a bandage over the affected area, he may have developed a further reaction to the tape. Some medications, especially OTC stuff, will stop being effective after a short while, so an alternate treatment may be needed.
In a situation like this, did you ask you son during your weekly calls (I don’t think that is too much to ask) how his feet were doing - for example, ask if it was it entirely cleared up? You could ask him to take a picture of it and send it to you, “just so his mom will feel better”. When you see that has gotten worse, ask him if he’s been applying the ointment, or taking the steroid, taking especially good care of hygiene, etc. Tell him to ask the doctor about the best way to apply anitfungal spray, how to clean and properly dry an irritated area, etc. before putting CLEAN socks on, etc. Be sure to ask about how long the recovery should be, when to follow up, etc.
And get him a new pair of shower flip-flops - the peace of mind for a couple bucks is well worth it.
I obviously don’t know how bad his feet are, or any details of his personal hygiene, and I don’t mean to accuse him. But it would not surprise me if he was one of those young men who, well, get a little sloppy when they go off to school.
One boyfriend of a roommate of mine in school developed skin problems because he was using too much fabric softener in his laundry, it wasn’t rinsing out, and he became allergic to the perfume scent. His athlete’s foot irritation provided the skin opening for the skin allergy.
Before you send him back after Thanksgiving, let him know how concerned you are, you’ll never stop being his mommy. Don’t forget to tell him how proud of him you are, because he is working hard, etc., lest you risk the chance of him feeling foolish/childish, and withdrawing.
The other suggestion is to let him know about times when you had to get medical attention for the first time for yourself on your own, how you felt better talking about it with your own parents since they worried terribly.
Again, I don’t intend for this to sound harsh or accusatory, I understand you are worried as any parent would be. I hope your son heals quickly, and uses this as a learning opportunity. Then tell him you want him to learn about how to deal with doctors, what questions to ask, etc. not just for himself, but selfishly, you want to prepare him for 25-35 years from now when he may need to be asking the doctor’s questions advocating for you.