TMI pain on left side

I had an ache where the circle on the picture is. (Left of my vagina) Just put my hand on it and felt it and I can feel a little ball. It's solid and it is very sore when I touch it or the press on the skin around it. 
 
I have no idea if this is where my ovaries sit or what it could be. Are there any experts that know the pelvic area well enough to say what it could be? 
 
I'm on my period so it could be swollen because of that I guess, but last week I had painful sex. My ovarian area hurt every time he thrusted inside me. The only time it didn't hurt is when I was on top. 
 
Any ideas please girls?