I'd try GTTTT and just see. If after good clarification and a little time, you still seem to be thinning, I'd ask your dr. about it.
Although it's young, 22 isn't unheard of for a guy to begin thinning, especially if it runs in his family. My BIL's brother started losing his in high school. It was so thin by his sr. year that he just shaved his head and has been doing so ever since. Not trying to scare you, just saying . . . . My five uncles on my mother's side were all bald on top by the time they were 25.
All this to say that if the dr. thinks you are actually beginning to thin/recede due to MPB, the sooner you start preventive measures like Rogaine, etc. the better if you want to preserve it.
Avoid wearing caps a lot - they don't help!