What Does Continued Vomiting With Headache In A Teenager Mean?

I have a 17 year old son, who is very fit and involved in open water swimming and triathlon. 5 weeks ago, he came home sick with vomiting. I presumed it was a bug, but 5 weeks on he is still vomiting. Some days in the morning every 20 mins for a few hours, other days feeling sick all day and vomiting 2-3 times throughout. He has no temp, or any other symptoms, except for a few headaches. He has lost 4 kg in the last 5 weeks, which now I am rather concerned. I took him to a doctor today, and she has booked him in to put the telescope down his throat. Are we doing the right thing? he is very frustrated and just wants to feel well, and get back to his training and sport.