Talk to Pediatrician on Severe Constipation

my 9 month old son is sevelry constipated.doc said give him more solid than milk.hes currently on bf 2 formula milk.i m giving him custard,souji ki kheer,pea apple carrot purree. i also add olive oil in his diet.now he passes stool daily but woh itna hard hota k he cry a lot while passing stool.or stool width ma itna huge hota k i m shocked k how hes passes out plz suggest me wat can i add in hiss diet or change formula milk ? pehly similac2 start kiya ta phr b constipation ti...now i switched to bf2 .....still same issue.