Many people report that GERD and heartburn get better on low carb. I know my DH has certainly seen a huge improvement in that area. Before low carb, Maalox and Pepcid were his best buddies. Now he never needs them unless he eats high carb for a day or two (like holidays).
Tums do have sugar in them, but you can try some of the over the counter (OTC) medications such as Pepcid, Zantac or Prilosec OTC. I believe of all of those, Pepcid is the fastest acting and any sugar or starch present in the capsules would be minimal.
Sometimes drinking a lot of water can stimulate excess acid production. How much water are you drinking? Other things that can irritate are caffeine, alcohol, carbonated beverages and many spices.
As Tofi advised, your best source of information regarding what's causing this and how best to treat it is your doctor, so do see them if this continues.