Hi,
I have two children a 2 and 1/2 year old son and a 5 month old daughter.  While I was home in AL where I had my son his peditrician always said that everything that was going on was normal.  My son is a grazer as she called him.  He was breastfeed and would change sides frequently. Even as a 2 and 1/2 he will eat all day he refuses to sit and eat everything at one time.  He will take a bite and run around and then go back and get another bite. 
I came on the road traveling with my husband after my son was 3 months old.  I always returned home for his monthly visits untill he was 1 year old.  Then my husband was relocated to NJ which was too far away from home.  The first peditrician that I saw up here was horrible to me.  He critized me for my son being so small.  He told me that my son had to put on weight or he was going to call DHR on me.  So I took a long 19 hour trip back home to my sons regular peditrician and asked her if he was too small once again and explained what had happened she told me that everything was fine and not to worry about it. 
Needless to say I did not go back to the man in NJ. 
I wanted to give him a piece of my mind but decided that it was not worth it.  I hope that this helps.  Take care.  I wouldn't worry too much about it.  Breastfeeding is good for your baby and they are supposed to be smaller than formula fed babies that is why breast fed babies usually never get overweight.