When should I be concerned?

I am 3 months postpartum & I breastfeed. I’ve had 2 periods since having my baby but this month I’m now a week late. I have had sex but to my knowledge my bd been pulling out. Could I just be late due to breastfeeding? I know I won’t know until I just take a test but I wanna hear some stories about periods after you guys had your little ones. This is my 3rd baby and I’ve breastfed them all and this is the first time I’ve had this happen. I’m usually pretty regular even after having babies and breastfeeding