I had sex in the beginning of the montth and I don't start my period till the end of the month and now it's the end of the month but I had my period but it was only for a day? And every month my periosd are always rite except this month

It could be that your cycle is changing if you have had sex it could be pregnant. But don't stress its probably the first thing but you might want to go to the doctor

I'm not sure how old you are, so more information would be helpful in order to give you more accurate advice.

Periods are never completely "regular". At some point everyone will be late, have a shorter/lighter or heavier/longer period. Lots of factors can delay your period, such as pregnancy, it could also be stress or diet changes, etc. If you're really concerned, the only way to determine is to be tested. Start with a home test and use it first thing when you wake up in the morning. Your other option is to call your doctor for a blood test to know for sure.

Thanks bekah876 :D