Difficulty in the bedroom

My SO and I are 17 weeks, 3 days, my stomach is uncomfortably big and hard already and no matter what we try I can't seem to climax because I'm uncomfortable. We've tried going slow, fast, different positions but no matter what my lower abs start tightening up to the point where it's painful..... almost like a charly horse in my abdomen...... Any suggestions would be much appreciated. I feel like it's way to early on to be having these issues. We're used to having sex at least three times a week and sometimes more than once a day. If we've got to continue on having this issue for the next four and a half months things are going to get VERY tough!!!