Periods irregular first time. Ovaries.

Hello Doctors, Greetings. I just turned 39 yesterday. I am slim and height 5.4. I don't have thyroid issues,nor diabetes. My HB is 13. My monthly periods occurs between the 28th to the 31st day every month. Last month it was on the 9th Feb and before that 9th Jan and before that 10th Dec and today I got my periods for the month of March that is the 6th March. I have noticed that in the month of Feb every year the Flow app gives me the correct date but I get my periods like 2 days earlier. As per the Flow app I was supposed to get on the 10th March. But I got on the 6th. This is for the first time it has happened. Pls advise, if this is ok for the periods. The flow is normal but scanty. I was under too much stress in the month of Feb though. As per my usg for yearly check up this year there are no cysts in my ovaries. Thank You