What Causes Itching At The Tip Of The Penis?

i had sex with a girl about 3 weeks ago and last week i realized that my penis was itchy at the tip after urinating(but it only happened once a day). i also realized that there were bright red spots on th head of my penis which are the size of a pin head each. they were about 5-7 spots on one side of the head. Yesterday i checked my penis and i could see some spots on the inside of the foreskin and they had spread across the whole head of the penis. i used a condo when i had sex