Not Normal... Maybe?

Okay so I had my son in October and i didn’t get a period until December about a week bleeding( I was working so he mostly bottle )January i have my normal 3day period ( I’m back to exclusively breastfeeding, no bottle.) It is now February and my period is 9 days late. I took a pregnancy test and it was negative but I’m extremely nauseous. I’m wondering if it’s from breastfeeding that i don’t have a period again and if that’s what causing the nausea 🤷🏽‍♀️ I’m not sure. Any ideas?