Every time after sexual intercourse i become very sore. usually for a day or two. what can be the cause of this?

Painful: Most of the time its from a lack of lubrication production. There are several OTC vaginal lubricants that can help. If you continue to have pain you will need to be seen for further evaluation.

Varies: Intercourse, if vigorous or rough, can lead to soreness. Also, make sure you are lubricated enough, either naturally, or buy some OTC lube. I dont recommend KY Jelly though as it is salt based and makes things worse in the long run.