Hi Joy,
You poor love. Heartburn/indigestion/gastric reflux is an awful side effect to pregnancy for many of us. Yes, it can just be caused by pregnancy and the effects are exacerbated often by what we eat. Basically that lovely progesterone is working it's magic and reflux often results.
If you have any doubt that this isn't indigestion make sure you see a doctor...

I wold like to add that it is important not to take any preparation that has aluminium in it when you are pregnant. Gaviscon and Rennies are very safe. Ihave used slippery elm bark powder with water added mixed to a liquid and this helped me. If it gets worse and it is likely - I would mention it to your care provider. You can take medication in tablet form that is like heaven to a bad reflux sufferer!