Oh, that pregnancy heartburn was the worst! My little toddler is running around now, but I still remember how sitting upright for 30 minutes after meals saved me. Try having small, frequent meals instead of heavy ones, it really helps and this phase will pass soon.
I had terrible heartburn in my third trimester, and I felt so miserable because I couldn't even sleep. What really helped me was drinking cold milk in small sips at night. Please hang in there, the moment your baby is born, this burning sensation vanishes completely.
I used to panic thinking my chest pain was something serious, but my gynac reassured me it was just severe acidity! Keeping my head elevated with two pillows while sleeping worked like magic. Don't worry, it is very common and completely normal.
Sending you a big hug, I know exactly how exhausting and painful that burning feeling is in your chest. Try having tender coconut water in the afternoon, it is so cooling and gentle. You are doing amazing, just a little more time to go!
No need to buy expensive antacids unless the doctor says so. Just have half a cup of cold milk, or chew on a piece of fennel seeds (saunf) after eating. Also, avoid lying down immediately after your dinner, take a small slow walk inside the house instead.