Hi welcome to Health care magic forum. Lactose intolarance is a term used to signify that there is allergy
to the intestine to the lactose normally present in the milk, what ever the sourse may be . mothers milk, animal milk, and formula milk, all contains lactose.
Some companies manufacture milk powders with out lactose, made from soya milk, which doesn't contain lactose, so if given to child he can tolerate it and there wont be any allergy and loose motions.
As it is a veining period you can slowly switch him to semisolid foods, like cerelac, overboiled rice, boiled potato, apple etc besides xero lactose milk.
Dont worry it is not a continuous process , after some time there will be complete cure for it, automatically. In the meanwhile he has to use some medicines like lactic acid bacilli, and enzymes for comfertable life with out zero lactose milk.
Wishing the baby a quick relief and thanks for calling.