As u r feeding the baby.
Feeding increases the hormone prolactin
in the body which suppresses the hormones responsible for menses. u will land into lactational ammenorrhoe which itself serves as a natural form ofcontraception
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.
Secondly if u are not pregnant then u can take pills for withdrawal bleeding.