Really bad heartburn or...

Cassandra • 26 years old. First pregnancy and I can't wait till Jan. 19th!
I'm 36 weeks pregnant with my first child and within the last 3 days have been having what feels like heartburn. A dullnpain under my left breast but I can also feel it fade over into the left side of my back as well. I don't eat much spicy foods and nothing is relieving it. Could it possible be something else... Or just really really bad heartburn?