What Causes Pain And Itchiness In The Vagina?

hi I'm 24 years old, i was in my second day of my period i went for bike riding just for an hour, after that my vagina hurts so much and also the muscles around it, and now after 4 days (the first 2days i had pain) I have painful itchy vagina and it also it burns when i go to bathroom..
also i dont use tampons, because last time i used tampons same thing happened, itchiness burnning around vagina area and also inside it,, i went to to my doctor and she gave me some creame.. why all of these happening to me...