underweight pregnancy?

I'm 5 feet and with my first I started at 92 was healthy and delivered at 120. I breastfeed for over a year and dropped down to 82 from breast feeding. I'm pregnant again and worried my weight is so low to start (10lbs below my first pregnancy). Has this happened to anyone else as in starting underweight? My bmi is only 16 - so worried ;( I eat great but I'm still breastfeeding