Irregular period

I’m 5months post partum and I’ve always had a regular period. Never been late other than pregnancy. Even after giving birth in March my period resumed with no issue in April. I tried birth control for only 3 weeks back in June and stopped before July.

Since June when I started my period comes every 2 weeks 😭 I have never had this happen before. This is my 4th period since early June when I tried out birth control. (I’m on it right now).

Has this happened to anyone ?