How To Treat Vomit And Acid Smelly Stool In A 2 Years Old Child?

My 2 year old vomited profusely for 7 hrs , 6 days ago. Vomiting then stopped until he had a single vomit 48 hrs later. He then had no further vomiting until this morning, 6 days after initial. He is also producing acid smelling stool, paler than normal which looks lie wet sand in consistency in his nappy. I presume it s a gastroenteritis type bug, but why does he appear to be getting better then keep having another vomit. Should I take him to the gp, ?? May need antibiotics as I am aware that bacterial infection can follow viral infection.