35weeks with menstral cramps in my back, contraction's?

vsprice1
I have had menstral like cramping in my lower back that hurts into my hips and around into my tummy for about 2hours now. There is always a dull ache, cramping comes and goes.It is painful at times, Should I be worried? I have been in bed resting for 1 1/2 hours and have had plenty of water. I drink about a gallon a day. Anyone else had this happen?