34 weeks pregnant and it feels as if I'm having a constant contraction. lol?

I was constipated for like 5 days so 2 days ago I took magneisium citrate to help me go. I stated having contractions later that night and have been having them ever since. I know they are not braxton hicks because they start in my back and wrap around, now my stomach is just hard and feels like a constant contraction.Anyone ever experienced this before? Oh, this is pregnancy #8 and I've never had contractions before my water broke before.