Welcome, here are a few things that should help:
- read the Newbie link at the top of the page
- Start charting your BBT using Fertility Friend
You probably ovulated later than you think and so your period isn't really 'late'. I had irregular periods before the pill too. Start charting, this will help immensly. Even if you are somewhat irregular, you can pinpoint when you are Oing and time sex better. Plus this will give you a good picture to see if anything is actually wrong. Good luck!