Help! 19 weeks Pelvic Pressure

I tried to call my doctor but I forgot it's a weekend and they're closed so I need some reassurance or something. I have been on my feet just about all day catching up on house work it is now mid day (3:30) and all of a sudden while I was giving my daughter a bath, I stood and got a tremendous amount of pressure in my lower stomach closer to the pelvic area, is this normal? It wasn't painful just a lot of pressure, it felt like if a weight ball was in my pelvis. It lasted a few mins and is slowly going away, I'm sitting down now. Is this just something tht happens?