I have heard of having more painful false contractions even earlier on with subsequent pregnancies. I personally had regular, painful contractions off and on about 3-4 weeks before I had my second baby. They would even come regularly, but they never got more intense or closer together, so I just knew it wasn't labor. I would definitely take cal/mag.
Are you able to check your own cervix to see if what you've been experiencing has lead to anything? If you are feeling very concerned, I'd er on the side of caution and get checked out.