Try different positions. You may be able to try and find something that's not so bad. It's actually healthy for you to have sex while your pregnant. But most importantly if you can't find anything comfortable, make sure your husband knows it's just the fact that you have a human inside of you! It's not him! Lol!
Low sex drive is normal. I'm 33 weeks and I don't have much of one. Sex has been painful lately, but I have noticed that if there is enough lubrication, sex feels good. Hopefully this helps