Small hard lump under the skin of my penis that isnt visible unless you look thuroughly and doesn't hurt unless squeezed. what could this be?

A few things,: But the most likely cause is a sebaceous cyst. These are benign skin lumps filled with keratin and fluid. They can be stable, or enlarge and get inflamed, and sometimes drain on their own. If you have a painful, inflamed, or enlarging lesion on the penis, see your physician for evaluation. Many other benign skin issues also present as lumps.