It's because the hormone relaxin relaxes the muscle that's controlling the opening of the stomach. With that said it can happen with any kind of food at any time. I need to sleep in an upright position when that happens, sometimes through the whole night. It's not very comfortable, especially not when I need to have my feet up high due to swelling :/
It comes whether I've eaten or not and no matter what i eat. tums usually works long enough to get to sleep. Your pharmacy might not help you if you ask. Mine said i needed to call my doctor... who never called back.
I use tums. I get acid reflex from anything I eat and its so random. I never experienced it before pregnancy.
Changing my diet and when I eat never helped me. So I took the extra strength Tums which helped for 10 minutes. The only thing that's saved me is Zantac (safeway brand). Both tums and Zantac are safe for baby. If you're curious about other brands ask the pharmacist. They have a chart of what you can and can't take during pregnancy!