Hi and welcome to the forum, sorry you're here on such crappy circumstances, but glad you've found it nonetheless because I'm sure you will find it invaluable in the coming years.
Also sorry it took a year to diagnose your son correctly, but these diseases can be very tricky to pinpoint and many people go years and years with no answers. My introduction to crohn's was pretty similar to his (same age, some of the same symptoms). I was going downhill pretty fast so they had to hit the disease hard with aggressive treatments right off the bat by starting me on Remicade almost as soon as I was diagnosed.
The only good advice I can give you at this point is to be well-informed on the most effective treatments and be your son's advocate to make sure he gets the best care possible. Don't be afraid to get second or third opinions if you feel your medical care isn't up to par. As much as we like to believe our doctors have our best interest at heart, at the end of the day, the only person you can depend on to make the right decisions is yourself.
On a positive note, it sounds like he is responding well to his medications so far and I hope he continues to do so! If you need anything at all, don't hesitate to ask.. we're all here for you! Best of luck!