What Causes A Lump In The Penis?

hello, i am 37 years old and do not have any histiory of serious illnesses in my family, i feel healthy and im a very physical person since i work in construction as a brick layer. I noticed a tiny lump underneathe the forskin of my penis. I am circumsized and i do not feel pain or discomfort or even any discoloration in that region. It is located on the side of the shaft and can be felt when the penis is errect only i am worried and embaresed to see a doctor about it. What could it be? and if it is serious what are the methods of knowing what it is?