As u r feeding the baby.
Feeding increases the hormone prolactin
in the body which suppresses the hormones responsible for menses.
So feeding will either cause irregular menses or ammenorrroeah.
But still if u have doubt of pregnancy
Get a pregnancy test done and pelvic scan done.
If it is positive then u can continue your pregnancy by consulting your gynaec.
take some medications from ur gynaec to reduce bleeding.
irregularbleeding is absolutely normal post delivery.