I Have Had Plaque Psoriasis For 17 Years And Have

I have had plaque psoriasis for 17 years and have been experiencing arthritis pains (annoyingly) off and on for many of those years. Over the past few months I have been experiencing severe pain in my right hand especially with regards to my middle finger and over the last month severe pain in all my joints during the night and especially in the morning upon waking. It gets better but it doesn't last, by about 2 pm I am in severe pain again and it just continues to get worse as the day wears on. I suspect I have psoriatic arthritis and have been doing some research on it lately and have come to believe that a toe on my right foot that has been twice its original size for the last 8 months (and I have bouts of pain associated with the sensation that it is dislocated) is also affected with the arthritis. I have also come to believe that the loss of range of motion and sometimes excruciating pain in my lower back is a result of its also affected. For the past 10 months or so I have been experiencing severe pain when I sit for any length of time and over the last few months I don't have to have been sitting for it to be painful, I just have to sit up from lying down or to sit down after being on my feet for hours and I experience pain so bad I never want to sit again. My question is: Could this pain I have been experiencing in my rear-end also be associated with the arthritis?