Lost my libido at the age of 18
So, I'm currently 20 and I have basically no libido. I haven't for almost 2 years now. I lost my virginity to my boyfriend (now my fiance)at the age of 17, and when we first started doing it, I wanted to have sex all the time. But then I went away to college and we had a long distance relationship. I still got horny quite frequently for awhile, but then it suddenly stopped for some reason. I know it's not that I've gotten bored of my boyfriend, because I haven't been able to feel horny for anybody. I don't know why this happened, but it's really hard for me, and it's been making me feel depressed. My doctor tested my thyroid to see if it was a hormonal thing, but the results came back normal. Has this happened to anyone else? I don't know what to do, but I'm so sick of feeling this way. Life just isn't as good without it, and I feel sorry for my fiance having to be with a partner who's not enthusiastic about sex ever. Help?