It is hard to tell what the big lump on the penis is without seeing it. The dimensions of the lump, its exact location (on the glans, on the shaft or on the skin close to the base) and the surface of the lump (red, purple, or white, with fluid beneath or not) might have been helpful.
The lump might be due to an infection. This lump is usually small and several others might develop in the area within a few days. If there is a rather big lump (several centimeters) on the skin next to the base of the penis, then you might be experiencing an inguinal hernia.
Anyway, visiting a urologist for a physical examination, urine culture and urethral swab is recommended to determine the exact cause of the lump on the penis.
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