I have this red bump/hard ball on the shaft of my penis under the skin. What is it? Should I be concerned?

Possibly a lymphocele, which is an enlarged lymph node on the shaft of the penis. We have lymph nodes all over our bodies and the penis is no exception. Lymphoceles on the penis often happen after frequent ejaculation and usually go away in a few days. If it doesn’t or if it becomes painful you should see a doctor.