I am having the same problem. I have been waking in the middle of the night with heartburn so painful that It puts me in tears.
Eating an apple before bed helps or even drinking milk. I have some emergency Tums next to my bed for nights when nothing else helps, but honestly they don't work that well.
Hope you find relief mama, it can be pretty miserable.
I eat tums....4-5 of them at once. What I found that works better though, and is better for you obviously, is to eat ice. I usually have a cup of ice in hand often. Sure, I have to urinate more, but it helps so much with this horrid acid reflux and keeping the vomit down so I don't mind so much running to the bathroom. Lol. I have two hernias, and during pregnancies it causes much difficulty with heartburn and acid reflex, as well as keeping my food in the back of my throat....so I'll take more urination over the terrible pain and sickness any day.
Nux Vomica seems to work best for me at this point, especially since reflux at this point (for me anyways) seems to be from a stomach sphincter opening and allowing acid to come up. Boiron has a homeopathic Acidil with nux vomica works really well too. I like that I don't have to worry about what's in it, and it works rapidly.
I'm going crazy and will try nux vomica. I think I have that in my stash. Sounds like tums will take just as much time and quantity as slippery elm. I crave ice in the third trimester so I eat that like crazy already but it doesn't take away the burn. It literally feels like its burning my throat. I'm glad I'm not alone but wouldn't wish it on anyone.
I get scared of anything papaya because the unripe papaya's enzymes are known to cause early labor..
Google it and you will know what I mean.
I am suffering from bad heartburn too and have no remedies :(
It is so unfortunate that they have made Tums category C drug during pregnancy :(