I feel a lump under the skin on my penis shaft at the base of glans. It feels like something hard under the skin. What could this be?

Probably not serious. Maybe sclerosing lymphangitis, which sometimes follows vigorous or repeated sexual activity. It's not serious and usually clears up on its own. Search online for more information; here's the Wikipedia article: http://en.wikipedia.org/wiki/Sclerosing_lymphangitis You can also find photos on line. Best to see a doctor to confirm; other conditions are possible.