You need to take a pregnancy test, four days late isn't really something to worry about because it did end up coming. Try not to stress out, go to the shop and grab a few pregnancy tests and take them. If any turn out positive then you should go and see your doctor. If your period keeps coming irrefutably you should ask your doctor for the pill, it will even out your cycle :)
If you don't want to get pregnant, protect your self girl!!!
Could be pregnant but by what you explain you shouldn't be so suprised lol. Unprotected sex leads to that usually all the time. If you don't wanna be pregnant if you start your period this time start some birthconrtol that way you dont have to worry about it. Also you don't wanna have unprotected sex and get pregnant but not wanna be pregnant and then have to put your body through the stress of whatever you decided to do about it. Just take a test its the only way to know for sure. Best of luck to ya :)
Aee you trying to get pregnant or no?