Hi PL,
When you are pregnant your baby takes whatever he/she needs to grow from your body. You could be deficient in vitamins or minerals. Have you has your blood tested for complete blood count, mineral panel, and b-12? You probably still take the pregnancy vitamins? Maybe not helpful enough?

Also vitamin C, calcium, and Vit D would be good to add to prevent cold and such. I know you are breast feeding, so please ask your OB/GYN doctor what you can do to improve your health, and to better your chances of staying well. Just and idea.