I was having protected sex. just after i ejaculated, i felt the tip of my penis itching. i checked for holes on the condom and there was nothing. what is causing the itch on the tip of my penis as i used a condom as it's been 4 days now?

Unsure: Was the condom coated with spermicide? (usually nonoxynol-9). If yes, maybe you are having an allergic reaction to that. Some people have issues with Latex condoms.

Irritation: Assuming that there is no sexually transmitted disease or infestation( Body lice, crabs), something is irritating the penile head, leading to the itch. Condom too tight, contact dermatitis from reaction to condom or its lubricant, trauma from contact against vaginal wall or cervix, etc. Try a different brand of condom, put a current condom over a couple of fingers, look for any cuts/sores.