Breastfeeding and pregnancy

Sorry if this is the wrong board. Is It normal for your period to come and go while breastfeeding? I’m 4 months postpartum and I had my first period after baby last month. My husband and I had unprotected sex during my fertile window as we aren’t too concerned with getting pregnant again. I took a test and it came back negative. Oh yea I am breastfeeding but i give baby a bottle of breast milk twice a day. So is it normal for your cycle to come and go while breastfeeding? TIA