Relationship strain!!

Me and my boyfriend of a year and a half used to have sex every day!! And it was still really really good. Now my sex drive has COMPLETELY disappeared

I don't like thinking about sex either. Every time we try I get distracted by my stress or fatigue. Its even worse when school starts again. If he does end up getting me to let him penetrate, I'm really uncomfortable and tight and it just hurts because of that, so we have to stop.

I'm attracted to him physically but I have this mental block with sex all of a sudden. We flirt with each other all day, and I am playful with him, but when it's time to have sex I just can't do it.

I am disappointing him every day and I he doesn't understand what's happening to me. I feel like an 8 year old who is grossed out by the idea of sex!! Its getting ridiculous and I'm worried my boyfriend will start to resent me. Is it hormones?? Should I seek a doctor out?? I'm 21 btw.

Edit: we've talked about this many times. He says he'll be patient and we'll try to figure out a solution. But he thinks i should be the one fixing it for the most part?