How do you know if you’re pregnant again?

I’ve been hungry a lot lately my baby is almost 4 months and I think I might of started my period last month but idk,I mostly pump but sometimes I breastfeed,I also working 8pm-4am so I’m not sure if it’s something like that should I see if I start my period this month or how does it work.I know some people get late periods and it’s not normal like before