Is heartburn a common early pregnancy sign?

So I'm 9 months postpartum and I think I might be pregnant again. I started spotting a week and a half before my period which was about 4 days after the end of my fertility window. On December 24th I started getting severe heartburn like I did during my whole pregnancy with my first I know it's not due to a change in diet as my diet hasn't changed. I've never had severe heartburn ever except during my pregnancy which makes me feel like im pregnant again. I can't take a test for another 4 days