Rapid unexplained weight loss postpartum

So I gained 60 lbs with my second baby, started pregnancy off at 165 lbs and went up to 225lbs. I wasn’t thrilled with my weight gain but when my milk (oversupply) kicked in I was losing the weight fast. I was back to my pre-pregnancy weight in 4 months… and now at almost (not even) 6 months postpartum I’m still losing weight even though I’m trying to completely stop milk production (I pump 3x a day for like 12 min but I’m still making around 40 ounces a day). That’s a whole other battle. I’m now thinner than I was before I even met my husband, and have lost 75 lbs total. Everyone is “happy” for my weight loss but I’m so concerned, so is my husband. I’m light headed, dizzy, nauseous, and get jittery when I have gone only a couple of hours without grazing on something. I’m not starving myself or dieting, if I want a whole sleeve of Oreos I’ll eat them. I walk a mile a day to get some fresh air but that’s it. I’m not weightlifting or running marathons, and no matter how sedentary or how I eat, I can’t stop losing weight. Has anyone else had this happen?