What Causes Vomiting And Excessive Crying In Infant?

Hi, Since morning my 9 month old son started throwing up everything and crying .We found that cough is also coming out when he vomits. I called up his pediatrician and he suggested to give him half ml Domstal. he did not tell me how many times i have to give him and is there any thing to worry? Note:-from the past 3 months he got sick(fever,cough and cold) in each month.