TTC- irregular cycles

This is my first time posting! Just joined this app, as my husband and I are truly wanting to conceive but I can’t seem to figure out my body & the other app I was using didn’t seem to be fitting for everything.

Little bit of background: I was on oral birth control (microgestin) for 9 years... in July 2018 I decided to stop taking it since my husband and I were married and decided to take the whatever happens happens route..on bc my periods were regular (the black arrow in the pic below shows 27-28 day cycle lengths) and they were always consistent.. since I stopped taking bc my periods have been all over the place.

Recently I started taking prenatal vitamins within the last 2 months and was wanting to start taking OPKs, but the last period I had was July 23rd & 24th (pic with red arrow) it only lasted about 2 days of moderate bleeding, I had very slight bleeding the few days before that but not enough to use a tampon..since then I have not started my period & the month before about the same thing..anyone else have this problem? When do I decide to go see the OB? Do I wait to try anything more?