Periods while breastfeeding

My girl is 10.5 months old and is breastfed still. I didn't get my period until around 8 months postpartum, and then I got a period the next month like normal. My period should have been due 4 days ago, but I still haven't gotten it yet. I took a pregnancy test one day after my missed period and it was negative. I've only had two periods so far so maybe it's too soon to figure out my new schedule but I'm still concerned. Could my period disappear again while still breastfeeding? I don't feel pregnant the way I did with my girl.