I am 20 years old and I smoke medical marijuana. Ever since I started, I have had to vomit every morning, and I get horrible acid reflux. Though there is no research linking the two, I can say that many of the marijuana users I have spoken to about this can agree they feel the same symptoms. Eating less acidic foods and following routines similar for GERD may help, as they did with me.
If he is really vomiting daily, then something is amiss. The doctor should have at least provided another consult doctor for you. I'd try another doctor soon to get some answers. The marijuana may simple being used to self medicate an underlying illness.