Nausea suddenly during sexual intercourse

Recently I have had sudden nausea and even vomited duringsexual intercourse. After my partner pulls out I feel fine and i'm ready to pick up where we left off but every time he enters me I suddenly feel sick again and can't enjoy sex. I havent missed my period yet but I am having a discharge that isnt foul though. It has been yellow or kinda brown but no smelly odor. I went to the doctor and she couldn't find any infection nor do I have a STD. Also usually before my period comes my breast are larger and fuller and painful but this month nothing. I'm not experiencing much cramping yet either. What could be wrong with me?[/i]

It maybe a kidnney problem, body chemistry problem. Check your ph and elecrolytes levels.