Heartburn is an early pregnancy sign for me. It kicks in about 2dpo and just gets worse. Things I've tried with last 2 bubs include:
* tissue salts chewable tablets from the naturopath. Only thing that 100% worked. Called Schuesslar acid neutraliser. Try a health food shop.
* gaviscon for when I ran out of the tablets
* things improved a lot when I started a GF diet
* huge wedge pillow in late 2nd trimester with DS1. It propped me up so I could breathe without choking on acid and meant I could still sleep on my back part of the night.

GL