Yes I do have AS and based on your symptoms and fused sacrum, it sounds like you most likely do as well. I am very sorry if that is truly the case, as it's a difficult thing to live with.
A lot of people with AS can have normal markers for inflammation even though that is not the case. My ESR and CRP are always within normal limits but rise and fall within that range depending on how I'm doing.
My ANA is a nonspecific positive, which is how I got my referral, but my rheumy doesn't care about that much.
Unfortunately, just like with any chronic illness, you will find some doctors who are strictly by the books, and some who look at the person's symptoms more to diagnose. Thankfully I was referred to a good one the first time, but with your fusion, I don't see why you would have any problems.