Confused help

Hello I'm confused you see my period has always been irregular to the point some times I would miss a month I went to the doctor's had a ultrasound and others tests apparently nothing was wrong except my folate is low.

Since may I have been having my period from at the end/ start of the month so starting on the 30th or 31st or 1st or 2nd ....and once on the 4th but it as always came at the start of the month but this month I haven't had my period at all my cycle has been any where from 26 days to 33 daye but this cycle it's 40 what's going on?