For the last 4 years I have felt something odd on my scrotum, I remember trying to look at it when I first felt it and it seemed to be a small black floppy blister or something. So since then I have forgotten about it, I have been single all this time so not bothered about cosmetics down there. But I decided to check it out again last night and I was a little scared to see it when I took a photo, it seems to have changed from a few years back. I am unsure if the flash from the camera is making it look stranger than it is. I have posted 3 photos for anyone who thinks they may know what it is, sorry to subject you to such a image. It can't be a STD because it has been a LONG time since I have been lucky enough to get the chance, ha. 

I am 33, very overweight. I first noticed it when someone threw something at me and it hit me in the nuts by accident, because I was in pain for a day or so, but I am unsure if the item hitting me caused a blister, or if it was there already and I only noticed it simply because I was in pain in that area so was touching it. 

Thanks for any help.