I had 3 months of irregular cycles and one pimple on jaw line. could it be pcos, hormonal imbalance?

Need work up to know: Reasons for irregularity include weight gain or loss, breastfeeding, alcohol use, eating disorders, marked emotional stress, endometriosis, uterine fibroids, cervical polyps, polycystic ovarian syndrome, excessive exercise & pregnancy. When a girl has just started menstruating & around the time of menopause periods can be irregular.

Possible: but doubtful. See your GYN for further workup and evaluation , including trans vaginal ultrasound, blood and urine testing.