Baby has green poop

My 3 month old baby is exclusively breastfed and has been having green poops for 3 weeks straight. I don't know why it's happening.. I asked her doctor on the first week and he said it was probably something I ate but I doubt it would still be going on for this long. I thought maybe she isn't getting enough hind milk but i usually pump first then feed and it's still happening. Advice would be much appreciated..