Upper Abdominal pain......23 weeks pregnant...OUCH?

I am 23 weeks prego. and having severe upper abdominal pains. Been to ER 2x's and called Dr. The baby is fine and flipping all over the place. Dr. told me to take Zantac150 and Maalox. Which I have been doing since I got pregnant. NOT helping! Hospital gave me a shot of phenegrin/demeryol and there again didn't help with the pain. I go tomorrow for gall bladder ultrasound. Any ideas what the problem is? This is my fourth child also.