Weight loss

Not sure what's going on with me............. if this is thryoid related or not. Anyhoo, I'm down about 5 pounds from my pre-pregnancy weight. I'm underweight. Mark's noticed, my mom's noticed, etc. I'm starting to get pretty worried about my milk supply. My mom said as long as I'm still staying hydrated and keeping my caloric intake up, I'll still produce milk. My chubby lil' girl seems perfectly satisfied. My clothes don't fit. I wore a shirt today that I bought after graduating high school. I'm definitely addressing this with my doctor at my recheck on Tuesday