When does period return after birth of baby?

So my baby is almost 3 months old. My period has yet to return. I have 2 other children and I never had to wait quite this long for my period to return. I'm especially getting concerned because me and my husband have been kinda fooling around (twice no protection) and I've been cramping on and off. Oops I know. But no other weird familiar symptoms. So debating on buying a pregnancy test to rule out pregnancy. If I'm not pregnant again, and my period still hasn't returned in the next month or so what should I do??

SN: my baby is exclusively formula fed so I'm not breastfeeding.