my OWN lack of interest in sex

Hmm, where to start..

Well I'm 24 and I've been with my man for 2 years, we are both mature, serious and exclusive. We talk about our future and our lives together very often and we're deeply in love... so I don't think there are any underlying relationship issues going on.

BUT, I don't have a libido. I love him, he's wonderful, I want to be with him all the time... but I just very rarely get frisky. When he initiates I go along with it, but often half-heartedly. It upsets me because I don't want him to think I'm not attracted to him. We have talked about it many times, and he is okay with it, very understanding and he never pushes me.

When we do have sex, I often experience pain or discomfort, especially upon initial entry. We have tried to fix this by using lots of lube (have tried several different brands, water-based, oil-based, natural and synthetic) and that usually helps a bit, but not entirely. This MAY just be because of size, but I would think that after 2 years my body would have adjusted to it. After the initial challenge, I enjoy sex. Sometimes though, I feel like I've had enough sooner than I would have hoped, and I want to stop. Often before either of us have orgasmed. We've also tried watching porn together, haha... but that didn't really go over well, he found it to be a bit awkward.

I have had a couple conversations with my obgyn, and nothing really came of it, and all my PAPs have been normal.

SO... I don't know if my lack of interest in initiating sex is because my body is remembering the pain from last time and "shutting off" my libido so it doesn't have to do all that again... or if it's an emotional thing, or a cycle thing, or an imaginary thing... haha.

Any ideas?