hard stuff growing on shaft of my penis ? help

[99_problems_right_here]

yea, so it was like 7 years ago when i first noticed this. i had somthing growing under the skin of the the shaft after a few month i can get it out but another one grows on a different spot along the shaft and this went on for like 4 years then after a while one grew longer 3cm under the skin along the shaft but i couldnt get it out cuz its under the skin and so 3 years have past and no growth happened , just this 3 centimeter hard thing under my skin . no pain but sometimes it hurts a bit during masturbation cuz the skin rubbing over the hard thing.. can you tell me whats going on?