Periods missed and gaining weight

Jasmine • Mommy to my handsome baby boy 👶🏻 Angle baby 12/24/2019 👼🏻 My love 8/29/2019 🥰

Does anyone know what I should do if I'm late for my period and if I've gained weight the past week more than I ever have? I just had my son in August and I haven't used any form of birth control at all but when I take pregnancy home tests they all come out negative. We've been trying for baby number two and normally my period is regular even after I gave birth to my son.