Erratic Cycles

Helen • A small teacher from Guernsey, UK.
Hi all,
I'm 31 (32 in December) TTC #1 and have been on BC pills since the age d 15 due to periods lasting too long (6 weeks +) as a teen. I came off of them a few months ago and my cycles have been:
32 days
42 days
40 days
37 days
I've been using the Clearblue Fertility Monitor and have had high days but never a peak. Today, CD10, I got a high reading. This seems a little early to me? I tested yesterday and it was low, now I have a high reading Glow has changed my cycle information and I'm apparently on course to have a 26 day cycle, far fewer days than my previous cycles. My fertile window wasn't supposed to start for another week, now it says I'm smack bang in the middle of it!
Should I just go with the flow and BD every other day just in case? I'm so confused! Has anyone else had experience of erratic cycles post BC? I've been off of them for five cycles now, thought it might have sorted itself out!