37 weeks pregnant feeling LOTS of pressure &....?

I feel like every time I walk, he is going to fall out.. I'm not sure if I should call my doctor or what... it's not getting any better. I've been having some contractions today, but I haven't timed them, so I'm not sure if its BHC. I went to the hospital last week for bad back pain & they sent me home & said it was caused by dehydration. I've been drinking plenty of water, so that's not it! I've been peeing a lot too, like A LOT more then what I usually have been. I don't want to go to the hospital again if this is normal. & I still have horrible back pain, worse then before. Help!