Mine did not start until I was much older - teens - but my younger brother had it from when he was a very young toddler. His was seasonal allergy related. Mine had an allergy component but was also emotionally triggered which I have learned to manage well. I don't really have any good info as far as websites etc but just wanted to give a

and say he is now a healthy 40 year old. In the early years my parents had many sleepless nights and trips to the ER. Mom has talked many times about she and dad taking turns sleeping in a chair holding him up on their shoulder so he could get to sleep. Also using a wedge in his crib during his worst season to keep his head elevated.
They found a great allergist when he was about five and I remember still her telling me that they learned about a filling cup example. My DB had a ton of allergies in addition to the seasonal ones; animals, mould, dust mites come to mind but there were others. The doc explained that he could tolerate maybe his dust mite allergy, but added some water to the glass for the rainy damp season when mould would grow under the leaves, then more water to the glass if he was around animals and more still during ragweed season - which coincided with the rainy, wet stuff. His system would overload (water spilled over).
The doc told my mom to manage how much water filled his cup. I remember I was getting a dog for my birthday, but had to choose a poodle (was the only non shedding dog my parents knew/liked at the time), my brother could not have carpet in his bedroom - too much dust was collected (for his 9th birthday he begged for carpet and got some ugly plaid that was the shortest, tightest pile imaginable - he was outgrowing some of it by then). My mom was a cleaning freak (my brother now says that was part of the problem - kids should be exposed to a certain amount of dirt/allergen to let them build tolerance - my mom just rolls her eyes, she's sure her efforts warded off attacks.) Of course he was on an inhalor as well. I remember that so clearly from my childhood. Intal - put the capsule in the chamber, puncture it and have him inhale it.
Mine is much more related to illness at this point in my life. At 16 when it started Hay and horses were big triggers to me and I was in equestrian clubs. As a young adult the emotional thing kicked in - when I'd cry my lungs would fill. Now it seems entirely related to chest colds. If I get any kind of cold with a cough it invariably leads to attacks and then bronchitis. I've learned to really watch at the first sign of a tickle and get tons of rest then and do everything possible to ward it off.
It is scary for you, but it is manageable and you'll learn what you need to - what triggers your DS and how to keep his environment as trigger free as possible. My DB also had an illness componenet but it was always worst in the fall when more of his triggers were present.