I was going to recommend the vinegar, lol. Don't know how you took it but it should be right before you start a meal. You can eat dill pickles as well. This will always help. You don't have too much acid in your stomach. The problem is you don't have enough to break down and digest your food and it is actually sitting in your stomach rotting. Have you ever left something in your fridge too long and when you opened the tupperware lid it spit at you? That's what is happening with your digestion. It is pushing on the esophageal valve and coming up because it won't go down.
Tums just causes more to rot and the problem is exacerbated. It may give you temporary relief but the heart burn/reflux will come back with a vengence. Your little one is also not absorbing enough nutrition and your prenatal is probably not disolving enough to do any good either.
Hope this helps. Congratulations on the little one!!!
M.
PS You can actually purchase stomach acid (Betaine HCl) at the health store if it gets too bad....Ginger can be used for comfort...