my 3year old son keep throw up he can't keep anything that mean water too can anyone tell what to do…

my 3year old son keep throw up he can't keep anything that mean water too can anyone tell what to do this not frist time this happened he get this when eat find things that he hide that old food that why it happens. help yall if take er all there going say is keep in only three day but the iv in his arms if cant keep it down