Such kind of small lump inside penis can be due to swollen blood vessel, Peyronie’s disease or Mondor’s disease. In pyeronie’s disease, a plaque, or hard lump, forms on the penis. The plaque may develop on the upper (more common) or lower side of the penis, in the layers that contain erectile tissue.
I suggest you to apply warm compresses on the lump and get it evaluated from a dermatologist.
I hope it helps. Take care and regards.
Isn't Peyronie's disease more on the surface. I also have a lump in the same spot. I only feel it during an erection, it is uncomfortable but not painful. This feels more like it is inside not in the skin or erectile tissue. I am surprised that a dermatologist would be consulted on this.