Missed Period while breastfeeding

Hi mga momsh, is it normal po ba to have irregular periods or missed period during breastfeeding. I'm 3 months postpartum and exclusively breastfeeding. Anyone who encounters the same situation or should I worry that I am pregnant again since sexually active ulit Kay mister and only doing withdrawal method. So far, symptoms that I feel are dysmenorrhea like feeling, cravings , insomnia and back pain