Before you began having sex, did you feel things when you kissed, petted, or made out with anyone?
Then there's probably nothing wrong with your libido.
I'll suggest something. You might just be finding penetrative sex at this point with this guy, an obligation. The part of you inside that is totally true to yourself might even be feeling a little used, especially if along with the sex being uncomfortable and not much fun, you also feel obliged to pretend to him that you're liking it so he'll feel good about himself. You should only have sex when you yourself are so turned on you can't hold back. "I have to do this to keep my boyfriend" throws the emotional brakes on any possible excitement.
And, if that doesn't sound like it, here's a good article on the relationship of thyroid issues and libido.
Km, are you talking about feeling stimulation inside your vagina? No one feels that - arousal comes from stimulation of the clitoris, which is outside the vagina. Many women can't climax with just vaginal sex, if they don't position themselves in a way to stimulate the clitoris during sex. The very outer portion of the vagina has nerve endings, but the inner portion does not, and that's why women can't feel a tampon unless it's coming out.