It's so great that you are still exclusively breastfeeding! I read just the other day that although the World Health Organizations and others recommend that babies be exclusively breastfed for their first 6 months, in the US, only 12% are! So you should be very proud!
Anyway, I think I remember similar puzzles when my daughter was about that age. I can think of two possibilities...
1. If you've given Miles any banana, that could have done it.
2. Maybe he's having a growth spurt and his body is simply using up every last drop of breastmilk.
When I tried to introduce solid foods to my daughter at that age, I thought she didn't like them because at first I was only offering her cereals. She just never took to cereal, but she loved gerber's prunes, fresh pureed spinach and mashed banana. "Prune" was one of her first words! So my suggestion would be to first make sure he's getting enough boob, and second, see if he wants to try prunes.