This is very common – more than you think. It's especially common for guys who are going through puberty. You've probably heard that puberty changes your body chemistry, causing you to sweat more, right? These bumps have to do with sweat glands, and they're entirely normal. Other bumps are the follicles of hair that has not yet appeared, and still others are acne, just like the pimples you get on your face. In all cases, there's nothing you can do about them. However, if you are sexually active and have bumps on your penis that resemble little clusters of grapes, there's a chance it could be condyloma accumulata (venereal warts). Though relatively harmless, venereal warts are viral and contagious and you should have them checked by a doctor.
If you're worrying about how someone might react when they see your penis in an intimate situation, relax – they have their own insecurities about their bodies and are probably thinking very similar things. As you get older you'll learn that everyone's body has imperfections, and when people get close they learn to look past that. If they don't they're probably too young to be having sex anyway. (For more, read JackinQ&A – Questions About the Penis.)