13 month old lactose intolerant? Or sensitive to dairy in general??

Eliza

13 month old was on whole milk for 2 weeks and promptly taken off due to MASSIVE BLOWOUTS on the hour if not more. It's been about a month since and his pedi and I agreed to try the lactaid. This is only night 1 so I cant say much as to wether or not hell blow out again, but I know hes been spitting it up randomly (though very little, but frequent) and idk if its bc its dairy again, or if bc he drank so fast.

Anyone have experience? I know lactaid is supposed to lack the protien. I had high hopes. I cant figure out why hed spit it up other than he drank it too fast.

Advice?