It sounds like an allergic reaction to something. Perhaps you used a lotion on your skin (a lubricant)or changed your brand of soap or touched yourself while urinating after not realizing your hands had been contaminated with a substance that you are allergic to. Think hard of things that have come in contact with the skin of your penis. If you can't pinpoint the source that caused the dots, then schedule an appointment with your doctor, preferably a dermatologist (skin specialist). An do know an allergic reaction will cause small red dots to appear, I got it one time after having sex with a girl and it appeared almost instantly. It took a day or two to completely go away. Good luck to you, sounds rather minor, just my guess.
Dont get really worried and think that its aids or anything like that because it probably isn't. If i were you i would look it up in a health book or see your doctor to make sure its nothing serious and maybe get something to treat it.
there...I think that covers everything...that'll be $100 for the consultation please.