HELP! 11 months postpartum and breastfeeding

Hi. :)

I am still breastfeeding and am 11 months postpartum. I have not had a postpartum period yet. With my first baby I got my period back around 12 months pp and got pregnant 13 months pp with my second baby. I have been having cramping, nausea, smell sensitivity, sore breasts, fatigue, etc. Taken several HPTs and they all look negative. I scanned my belly at work (I'm a labor and delivery nurse) and think I saw something on the scan. Could I be pregnant and still getting negative tests??