Back Pain and PA

Hi, I have had Psoriasis since I was 18 (now 45) and for the last 7 years I have had bad pack pain (upper, lower, neck and shoulders). It used to come and go with long periods of no pain but now it is almost all the time. I have always put it down to stress, bad posture, not enough exercise etc and no one has been able to pinpoint what it actually is. Someone sent me some information the other day about back pain and inflammation and of course this had PSA on it. I had never thought about this before (and no one has ever made the link or tested me for it). But I am wondering if back and neck pain can be a dominant symptom? I have one middle finger that I sometimes feel joint pain in and my big toe can get a really bad shooting pain if I bend it sometimes. My knees sometime hurt if I walk down steps. But all this is very subtle compared to the back pain and no obvious swelling. I get back pain, incredible stiffness sometimes and weakness. I am so tired when its bad too. Could this be PSA? I would love to hear what people think?