It seems like he is having intestinal worm infestation. Please get his stool routine test done to look for ova or cysts.
Consider giving him a dose of deworming medicine like albendazole
. There may be occult blood loss in his stools that is making him pale.
causes green stools and diarrhea
. Get him checked for this too.
Please get a second opinion
from another doctor. This is definitely concerning. I do not think it is because of growth spurt.
I wish him speedy recovery.