How can I explain PSA to my older brothers (77 and 80, both still active) and friends?

Can someone please tell me how to explain to my family and friends what psoriatic arthritis is and how it is limiting my life? They either don't understand at all or they brush it off with, "Oh, everyone in our family has arthritis." Friends continue to ask me to do things I did before but can't do now, like go for a walk or spend a weekend camping, walk through an art fair on a hot day, etc. Two years ago I was fine. I was 68. Now I am 70, have full-blown PSA, am needing to use a walker to walk more than a block, am in constant pain and not sleeping well. It's not 'just arthritis." How can I explain it? It came on like a tornado a year and a half ago and never let up.