A yeast infection is just an over production of yeast. Nothing 'happens'. It can itch like crazy and smell like you are baking bread in your hoo ha. I am amazed your doctor didn't give you something for it - considering it has been an ongoing issue with you.

There is medication to help it go away. Some women prefer the natural route though. Not me. I want medication to get it over with right now.

I've never had one but there are omeds you can buy at the pharmacy. I don't think they do any harm even if you don't have one. Maybe get one and use it and see how you feel after.

If a yeast infection was the cause, I would think that it would hurt even when you are on top.

This is probably waayyy out there..But..When I went in for my first ultrasound and exam what not, I was told I had a tilted uterus(retroverted) and apparently some girls are just born with it and others get it after they give birth. Like your uterus just switched positions or something. And for some women, sex can be painful as well as inserting tampons. That is probably not your case, since your son was born 4 months ago, and i'm sure if that *was* your case, you would have felt pain after he was born. Or your doctor would have informed you...I'm rambling now..I'll stop..

I have a tilted uterus and sex hurts a lot for me sometimes too

Go see a doctor to rule out a UTI or Pelvic Inflammatory Disease. All these may cause Dyspareunia (painful sexual intercourse). If you are found to have the above, take anti biotics(Doxycycline Ciprofloxacin) and Pain killer (Ibuprofen)
You will be fine with in a week.