cramps

What do braxton hicks feel like? And when do they start? I'm 18, almost 19 weeks and I've been having an awful cramping/muscle tightening sensation in my lower abdomen on and off for the last 3 days. No bleeding, just cramps. I'm going to the ER when my husband gets off of work, just wondering if anyone else has dealt with this. I don't think it's anything major, bc I feel consistent movement from baby.. It's just extremely uncomfortable and Tylenol only helps so much.