Irregular periods?

Kaitlyn

I am 4 months postpartum from having my baby. I don not breast feed. Are periods irregular after birth?? I cant be pregnant we use condoms or we pull out 1 min before he has to cum and do a hand job (sorry tmi) but I am 11 days late. The last cycle I was 5 days late. I have took pregnancy tests and did a urine sample at the doctors and it all came back negative