Few days back i found blood droplets in by white boxer, i am not sure where the blood came from, but i guess it's from the penis.... i am 22 years old?

Follow up: In young men who present with spotting in their underwear, the most likely cause is a urethral stricture (scar tissue in your urine channel). The cause of the scar tissue is usually unknown, but may be from trauma, STD, etc. if you have noticed a decreased urine steam or going more frequently, these are seen with strictures. You should be evaluated by a urologist regardless.

Possible: from low grade infection, masturbation or intercourse. You must be examined and get a routine urine analysis and culture.