Please Help!

I am 26 weeks, close to 27 and yesterday I had some liquid gush out of me, I don't believe it was pee, but it soaked my underwear and went through my pants a little. I had some cramping, I called L&D;, they had me walk around and after 2 hours I hadn't had any more leakage. I've had some discharge, then tonight I've had super bad lower back pain and now I've started cramping pretty bad. When should I be worried or call my Dr? This is my first, I just want to be safe, not sure if I'm overreacting or not. Update! after being in some pain all night, I've been cramping constantly today. Just took a warm shower and I think I feel a little better, baby is moving around okay. Still not sure when or if I should worry.