Breastfeeding not exclusively

Hi mummies. I have been latching my daughter and also mix formula. I got my 1st period after i give birth 7 months later which was on Apr/22. May/22 yes and on jun/22 no period. My period continue Jul/22 and Aug/22. Now Sep/22 I’m 7 days late. Is it normal? Or am I pregnant again as I’m feeling nausea most of the time now. Advice pls!