PTSD?

Idk if anyone can help me on here, but I'm in the army. I am almost finished with ait (advanced individual training) and I have been feeling really weird lately.. can't sleep, when I do I jump out of bed randomly, not eating as much, bed sad a lot, and get easily adjetated, space out a lot, and when I went home on emergency leave, I went to the zoo to calm myself from what was happening with my family situation, and got totally freaked out in the history room where there were a lot of people in a tight space (never really been a claustrophobic) I just felt overly anxious and practically ran out of the room. It's been bad enough that my sergeant came up to me and asked if everything was okay because he's noticed a change in my behaviors and stuff lately. This has been kind of effecting my relationship with my fiancé, we barely talk since my training is at night and he's day shit, and when we do talk I feel as though I'm boring him.. we talked it out and he thinks I might have ptsd. I haven't done much besides basic training and ait which both aren't terrible. I'm 20 and this is my first time being away from my family and friends like this. Does anyone know if he could be right or what is wrong with me? I don't want to go to the doctors or counselor yet, in fear they might medically discharge me, so I want people's input. I completely understand if no one can help since this is a completely different app than I should be posting on, I just don't know what other thing to use.