Sorry to hear about the struggle. Some of my friends with Lymes report very similar symptoms as SpA, so I am sure misDx happens a lot.
What spondylitis means for your son -and you- is difficult to say. Some people have a very difficult time and some have a more mild case. some go through long periods of low disease activity.
Your son is blessed to have you. believe it or not, several parents believe the first doc that says "it's growing pains" and don't explore any further. Now that you know, you will know what helps and what doesn't. smoking, drug abuse don't help. being active does. there is no cure (yet) so the meds wont solve everything, but they help a lot of people live normal lives. Now that you know, you will also know what complications to watch out for and guard against.
If your son is a teen, then check out the SWIFT site http://teens.spondylitis.org/
There is a ton of info on this www.spondylitis.org
site. The last issue of Spondylitis Plus magazine has some articles regarding Juvenile spondyloarthritis. call me & I'll mail it to you 800-777-8189.
another helpful thing for you to try is going to a support group meeting. there is not one in WI, but perhaps next time youre in NY or another state you can check it out. You can join my group via skype if you want. let me know, because I have to get it ready. http://www.spondylitis.org/patient_resources/support_groups.aspx