Ovulation advice please!

So I need some advice or thoughts:) I've been off my birth control since August and before bc I was normal 28 ish day cycle. And my cycles went 28, 42 and 40! So this month I have been using opks and started testing cd12 and I got a positive on cd14-15. Why are my cycles so long if I'm ovulating earlier than i thought? Hope this makes sense!