I need any advice you can give me

Ok so af came 4 days late she showed up on the 30th and ended on the 2nd so only 4 days long. Ok here is where I need the advice on the 6th I was feeling odd like I was starting to ovulate so I took a opk on the 8th and I got a positive but the app said I should start ovulation on the 13th. So that only left me one day from the end of AF to when ovulation started has this ever happened to anyone else. I don't know what to think any help will be great thank you