Worst pain of my life!

I am having the WORST lower abdominal pain...mostly on the left side. And extreme lower back pain. I also have the frequent urge to urinate, a burning sensation when I urinate, and only a little bit comes out at a time.
I called and left a message with my OB to see what I should do.
But have any of you ladies experienced this?
I'm in pain to the point where it's uncomfortable to sit, stand, lay down, or be in any position for more than 5 minutes.
26 weeks pregnant and no medical problems.