How Can A Penis Shaft Lump Which Is Movable Be Treated?

i have a bump on my shaft about midway down. i noticed it after a night of masturbation about 10 seconds in. it is not painful but is movable. because of my concern i got a std test and was clean. ive had it for more than a month about now and went down alittle. is there any way i can get rid of it, medication, cutting it, or etc.