I had heartburn towards the end of my pregnancies, maybe in the last month or few weeks. It seemed to be most noticeable at bed time when I was lying down in bed. It was never really that bad. Nothing a QuickEze couldn't fix. I didn't put on a lot of weight in my pregnancies, so that probably helped.
I had dreadful heartburn during pregnancy and followed the same regime as yourself…..until the Chemist wouldn't sell me any more antacids ! Eventually spoke to the doctor about it and she advised me to cut out the Bulgarian Black Current jam I was having on my morning toast with a hot cup of tea. The heartburn subsided.