Incorrect! The reason is this! you usually ovulate 14 days before your next period - and a day or two on either side of the day you ovulate are the fertile days! So in someone - like yourself - who's period is irregular and her and there! This means that your ovulation can also be here or there! So you could have ovulated 4 days ago - when you had unprotected sex! I am ONLY saying the IF's I don't know OK! I don't think you are pregnant, BUT these things happen - and you both need to know the facts. So IF and I mean IF you ovulated 3 days ago and there was sperm, but you get your period tomorrow - it was like not enough time for your brain to get the memo that you had conceived - the action of your period had already started - does that make sense?
Also there is something called "vaginal bleeding" this is what you hear about when women are pregnant and have "periods" it is the loosening of uterine lining build up! It usually happens - when it does - the 1st couple of months before the body gets in sync! So within a couple of weeks IF you still haven't gotten your period you WILL need to be checked out! IF you do, I still want you to get a check up - as I think you should be put on BCP's to regulate your period! Please let me know how you make out OK? Good look honey!