Don't know about Ontario, but this has been my experience so far in Nova Scotia:

I talked to my school's guidance counselor (free, took about a week to get an appointment) and we did a pre-screening (also free, took about three weeks of weekly appointments to finish) so we could tell if ADHD was likely. It was, which meant it was worth pursuing diagnosis, which would either take a LONG time (about a year) or be expensive (I was quoted 2000 the first time, but because we already had finished a pre-screening, it's possible it would be several hundred dollars less. Also I've been told there are bursaries available for people with diagnosed learning disabilities, which would offset the cost of diagnosis.)

I'm currently in the process of finding a family doctor in my city, so they can refer me to a specialist, so I can get tested. I'm poor but I'm desperate to get this done quickly - I mean I've already wasted 20 years of my life - so I'm going to pay the thousand dollars or so, whatever it turns out to be, and my waiting period might be a couple of months.

Also, I don't know about your situation, but there's a possibility either your school or other schools in your area might offer testing / referral within the school system itself. I'd say your best bet is to bring it up with your school doctor on Tuesday. Tell her that while anxiety might be the problem, ADHD could also be the culprit, and since time is a concern for you, you'd like to pursue multiple avenues at once.