Ok - this is my advice - someone else may have an opinion.
I think you need to forget about how many days your period lasted - I think you may have just had a freakishly long one!
Your 2 normal cycles were 26/27 long so lets start you with an average 28 day cycle to make things simple - ok?
If I were you I wouldnt bother counting now until you get your next period. You're cycle must be a bit f'd up if you had such a long period - was that all FULL FLOW??
Then count the first day of your next periods full flow as day 1 (CD1) and say you're gonna have a cycle length on 28 days.
Until you get your next period I dont think you can properly estimate when you will O so just BD every other day until your period comes.
Any one else got any ideas???