HEARTBURN!! OUCH!!

I'm 36 weeks pregnant and my heartburn is getting out of control. I can't get any sleep because it gets so much worse when I lie down. I have tums but they won't work. I took a cap full of Pepto-Bismol and I just regurgitated lots of stomach acid and some of the Pepto-Bismol. All I had today was a bottle of water and a bowl of mini-wheats for breakfast. I'm in so much pain and my throat & chest are on fire. Help..?