ESR is often elevated with ankylosing spondylitis, but not always. Have you had an Anti-nuclear antibody test (ANA) to rule out Lupus or other similar conditions?
Many/most people with ankylosing spondylitis have trouble breathing... is this one of your symptoms?
If you have the HLA-B27 marker, which is often present in arthritis type conditions, it's possible you could have AS... From what I've read, AS is rare in those without this gene, but I could be wrong.
There is no specific test(s) to diagnose AS, but imaging can help, if your doctor is willing to order the tests. The important thing with AS is to maintain your ability to remain mobile or you can become completely debilitated. Physical therapy can help, as can deep breathing to help keep the chest open. Swimming is good exercise if you have access to a pool/water in which to indulge... Talk to your doctor about this.
Good posture is imperative as is good sleeping posture. Again, your doctor can help.
It's important to note that these things can also help with pain caused from other forms of arthritis or from pain caused by Hashimoto's. If your pain is from Hashimoto's/hypothyroidism, it would mean your dosage of thyroid medication is not adequate.
If you have Lupus or ankylosing spondylitis, there are other classes of drugs that can be used to help with the pain, such as Humira, Enbrel and others. These drugs come with a lot of adverse side effects, so it might be best to try other anti-inflammatories first, to see if you can get relief before resorting to them.
Do make sure you have adequate testing/imaging to insure a proper diagnosis.
You can have seronegative rheumatoid arthritis. This can also change overtime from negative to positive. My rheumatologist did a HLA-B27 (main gene associated with susceptibility to ankylosing spondylitis) blood test as part of my work up which was negative thankfully.
I do have stiffness and pain in my bones and was in a bit of a panic that I might have the start of rheumatoid arthritis but I just found out my vitamin D levels have gone down to 59 nmol/L (23.6 ng/mL) despite taking 3000 IU daily. I have absorption issues as I also have other deficiencies including iron anaemia.
From the list below I have Hashimoto's thyroiditis, autoimmune pernicious anaemia, alopecia areta, vitiligo. My sister has the same four autoimmune diseases. We also both developed Hashimoto's thyroiditis last (hopefully last!).
Excerpt from the book "The Everything Guide To Thyroid Disease" by Theodore C. Friedman, MD, PhD and Winnie Yu Scherer:
"Although the majority of people with Hashimoto's will not develop any other disorders, it's important to know what some of these autoimmune conditions are in case you do start to experience symptoms. Keep in mind, too, that you may be more likely to develop Hashimoto's if you have one of these other conditions.
Type 1 diabetes
Systematic Lupus Erthematosus (SLE)
Inflammatory Bowel Disease
Multiple Sclerosis (MS)"