Why do I still get irregular period?

I have been to a female doctor and there was nothing wrong. I find it very annoying how to know when my period will start.

by the way I am still a virgin.
Been having issues with sleeping. Begins on 28/07 and Stop 3rd/08 Typical cycle length 27.5days. the typical period length of 5.5 days.

Typical cycle length variation of 5.3 days.

It sometimes comes early sometime it come later.

I have already been to doctors. They didn't really do anything part said I already had a blood test.

Got the information from app called clue
Why do I still get irregular period?
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