Anyone else had this before, I don't know what it is...

I keep getting a pain sort of in my groin but going down the inside of my thighs. Feels like all of a sudden I've pulled a muscle. Happens sometimes when I'm just walking along, or sometimes just standing even. Comes all of a sudden and makes me gasp and have to stop walking and try and change position til it goes away.

Just wondering what it could be?