Yeah, it definitely varies for me. In the first tri I thought I would never find my groove again, but thankfully things have been better since.

The watermelon stomach makes for some interesting positions, and the stretchies mean its almost always lights off these days...DH doesn't seem to mind though.

I find the hardest thing is getting in the mood...I never used to take so much persuasion.

I think its best to be open with your partner about it and explain how you're feeling. Then try and drag them to bed at YOUR bedtime (which is really early for poor DH). Its one of those things that I think is important to work on...but it takes some understanding from your partner...don't stress or over-think it. The worst dampner on a woman's drive is her brain! Go with how your body feels and don't be afraid to admit you're finding it tough at the moment.