Allergic to milk ???

My son is a year & 4 months and the past month or 2 he’s been puking his cow milk , not sure if he could be allergic to cow milk ?? Or just lactose ? But I read online he could be since he pukes it every single time he has it to go to sleep . Or when he coughs he pukes the milk . But once I give him juice or Pedialyte or water he won’t puke that ..