Ouch!

I'm 15 weeks along and everytime me and my boyfriend have sex I feel a lot of pressure in my pelvic area. Its not pain, necessarily but i just feel so much pressure.

We've tried different positons... Such as from behind, me laying on my side facing him and facing away... Him on top isn't really an option because I'm not comfortable on my back and it isn't good for you to be on your back anyway from four months and on, so I've read. Even if I'm on top, I feel like there is too much of him inside me, even when it isn'tthe whole thing,and I feel that same pressure.

Any suggestions?!