tums is safe for pregnancy its just a boost of calcium which is great for babies growing/hardening bones. If you want the alternative milk ie. milkshakes, ice cream, I have heard a lot of women eat mint ice cream or just a tall glass of milk. try to avoid spicy foods, don't eat before bed, and use a few pillows to help prop yourself up when laying down.
I don't know how well it works but ive heard to lay on your left side. Tums are great tho too and safe. it could also be nasal drainage in the back of your throat. I have allergies and since becoming pregnant they have gotten a lot worse and it feels like what your describing. Hope this helps.