Absolutely terrible heartburn !!!

I'm 37w5d and my heartburn is AWFUL. Every time I've ha sit my whole pregnancy it's been terrible but now it's ridiculous. Just from yawning I get it horribly. It's very painful and won't go away; even drinking water and taking tums does big help. I cough like crazy in pain from them. No clue what to do, I get it for long periods of time, half of my days consist of it.