If you don’t have sex with girls and you still get infections on your penis then the reason is probably lack of hygiene of your genital region. Masturbation with dirty hands can also cause penis infection. Feeling the heartbeat and “nerves in the legs and arms” is probably due to the pleasure of getting an orgasm. Harder masturbation may irritate the skin of the penis which manifests with swelling. You may try masturbating a little gentler.