I wish I had that problem. If you are breast feeding and eating/excercising like you were pre-baby its probably just the breast feeding. It speeds up your metabolism. If you are "too" skinny, I would suggest getting in to see a doctor. They may have some suggestions.
I also lost 45 lbs (beyond my pregnancy weight) after having my son, breastfeeding is a wonderful thing isnt it for so many reasons! You might increase your fat intake (good fats like avocado of course) and your overall amount of food. When I was breastfeeding I was an insatiable beast! Ive gained back 8 lbs now that im done breastfeeding. If you are really concerned you should see a doctor and probably have your thyroid checked. I know that diabetes can also make you lose too much weight if its not under control
I would get your thyroid checked. It can get off whack after a pregnancy and one of the symptoms for an overactive thyroid is weight loss... do you have any other symptoms like a fast/irregular heartbeat, fatigue, sweaty palms or feel hot all the time, hair loss, trembles (hold out your hands and see if they are shaky)?? I would see a doctor to run tests, def. make sure they check thyroid though... it's just a simple blood test.
Try for healthy fats, and lots of them. Avocado, nuts, salmon, and whole milk yogurt are all great sources of fat. I agree you should speak to a Dr. though, just to rule out any other possible medical conditions. Good luck!
I had the same problem. When I got pregnant, I was a size 5-7, 135lbs. Now I'm 3-5, 115-120lbs. I found out after I had my daughter that I have a nodule on my right thyroid that has caused me to drop all the weight. I gained 60lbs with her so all together I've lost 75lbs. If it is a problem with your thyroid, there are other symptoms to go with it. Just google hyperthyroidism. You may try drinking ensure with your meals if it's ok with your dr.