I'm 18 weeks pregnant now and I'm having a heartburn that can last until the next day. Is it normal?

Yes normal! I’m on daily omeprazole for reflux/heartburn/gastritis so the doctor changed it to famotidine (which didn’t work for me). In the evening, the reflux was the worst, I could not lay down to sleep and it hurts super bad! Needless to say my dr changed it back to omeprazole after he consulted with the pharmacist to confirm that it’s safe for pregnancy and breastfeeding. Been on it ever since but I do still get reflux though not as bad that I can’t sleep. You can ask your OG dr for options and see what works best for you!