Difference between Heartburn, acidity and nausea

I'm 27 weeks now. Lately I have been having this feeling of my food till my throat. I thought it was nausea/indigestion. So when I mentioned this to my doctor today and she said use tums . And it cured me too. But tums description says for acidity or Heartburn etc. So now I basically think I don't know the difference between Heartburn acidity and nausea. Could someone tell me