Here're some methods that work on me:
1. don't eat fried / oily food
2. drink some milk whenever you have the "burn" feeling.
3. don't eat a few hours before you go to bed.
4. don't make yourself too "full" every meal
I have stomach ache before pregnancy, I don't know if it's the same for pregnant women too.
1) eat regularly
2) eat less every time and eat more frequent (less burdern for the stomach then)
3) very important, don't eat something that's difficult to digest - maybe even you don't know what are they, but after you eat them and feel uncomfortable for the stomach, remember to avoid them next time.
for me: skin of apple (can remove the skin before eating), 青口, 魷魚, 豬耳, 難 "jiu" 嘅嘢食.