When you lay on your side put a pillow under your belly/side.. It relieves a LOT of pressure. You can put one between your legs too & that might also help
I think that could be baby, you're just over half way through your pregnancy and I noticed that whenever I laid on my side, it was as if someone was putting weight on it, making it heavy and uncomfortable... I basically wrapped myself round my pillow and that took the all the uncomfort away. I put it all down to baby, so it could be the same for you:) Good luck & wishing you all the best. X