Might sound gross but try pickle juice. This is my 4th pregnancy and when tums dont do the trick pickle juice usually does.
my dr told me to take pepcid i get it really bad also... sometimes the pepcid doesnt even work well.. but it does alot better for me than the tums... you can also take zantac... but if you worried you can check with your dr...
I had horrible heart burn with my first baby, Ive had it this pregnancy but not nearly as bad. I had to sleep sitting up for the last two months, and the only thing that would make it better was maalox, its the liquid heart burn medicine (only the berry blend worked for me).
Also, the only thing that truely made the heart burn go away was delivery:)