Is it normal?

Hi i am exclusively pumping due to unable to latch my bb since his birth, my period came back when im 3 months pp and my period cycle become 24 days. now im 6 months pp. and my period is late for 3 days even though i feel cramp too. Went to test and its show im negative for pregnancy. Is my period still irregular during pumping of milk supply? need some advices. TIA