If it could be herpes, it might be that. It's also possible to get pimples on the penis. I guess the basic question is, does it look like a pimple or a cold sore or a wart? Search for photos of each to compare if you're not sure. Or describe it in more detail.
A hard lump under the skin sounds like a cystic acne nodule, so a pimple would be my first guess, but you really didn't say enough to have any real idea.
Monty, First google boils, and look at images, if there like yours then thats what you have, have a look down the matches and see if theres a NHS one, there pritty good, and take it from there.
If its not like a boil, try herpes, and do the same.
Good Luck