have you tried going to a chiropractor? I do some "round ligament releases" on my preggie patients... sometimes massage therapists who specialize in women's health and pregnancy know these releases too. you can try it yourself, depending on how much you can handle, it can be painful. it's hard to describe, but i'll do my best...
if you feel around where it's sore/where it cramps, you may feel a sore bump. you press slightly in to your abdomen and upwards toward your shoulder (if you're doing it to yourself, you'll almost be "pulling up" under your belly with your index and middle finger. essentially atttempting to stretch that ligament out, not just compressing it...) you can do this starting out seated and slowly stand while doing the "pull". (i know, easier said than done) or you can just lay on your back and maybe have someone do it for you (they could either stand by your head and 'pull' up or stand at your knees and push up...
again, be careful not to push IN. you're just applying enough pressure to cause tension in the ligament to stretch it.
I'm not currently practicing because i'm home with my 9mo old, but if you live nearby, maybe I could try it for you if you can't find anyone. Just let me know!