Can anyone help?

I think your best idea is to consult a doctor about the pain in your upper back, and get an examination and diagnosis. I do not see any way that someone can remotely diagnose your pain and further tell you if it is related to , or caused by, your psoriasis (which I assume has been diagnosed by someone medically qualified). Additionally you have no idea who anyone on here is or what thay actually know - even if they said "yes that is xx and it is caused by your psoriasis" - what would you do next?

Wendy: with respect, I really think you should avoid possibly/potentially alarmist guesswork about someone's health by speculating on specific conditions.

Wendy: you say "It is only a couple of years ago that I had the sort of lung problem that KT described. " KT described a pain or discomfort - YOU decided it is a lung problem - you have little or no basis to do so. You might have read a lot of wikipaedia pages but that does not make you an expert. No ethical or capable doctor or medically trained person deserving of any respect would jump to a definite warning of pleurisy or lung problem on such little evidence, and no knowledge of the person's medical history, it would certainly be irresponsible and perhaps even have a negative outcome if they do. And yes, I wondered about a specific medical issue for KT, but I appreciate the importance of not unnecessarily alarming someone about whom I know nothing. Many people come on to a forum such as this because they are desparate or have no idea where to turn for advice, and for some reason may not have not approached a doctor in the first instance. Some asking the "could this be xx or yy" type of question might even have hypochondriac tendencies, and certainly many coming here are potentially desparate and vulnerable. (such vulnerabilities are traded on of course by the numerous websites offerring guaranteed psoriasis cures or total symptomatic relief if you buy their books and subscribe to their paid monthly channels). That is one very good reason why I do not try to diagnose based on a few words in a forum.

wendy: I also have "science qualifications" and also medical qualifications and I understand enough to know what I do not know. I have also had a serious lung infection quite recently - but that does not mean that I am going to diagnose others' symptoms. "Advice" is something along the lines of "you really ought to consult a doctor" or "do not rely upon what unknown strangers on a forum like this diagnose for you, whatever they tell you you, your next step would be to consult a doctor anyway, so why not simply do that in the first instance?" "you sound like you have pleurisy or other lung infection" is not advice, and it is potentially not even helpful - it is irresponsible speculation.