Psoriatic as the other types of immune-mediated arthrtitis is inflamation in the joints by unknown cause. Sure sign for psoriatic arthritis is the nail pitting, also secondary signs are negative RF (which rulez out RA), distal joints of the fingers and toes predominance (the joint closest to the nail), and also 'upper and lower extramities are affected equally'. There are 5 types of psoriatic arthritis, the most common type is that which affects the large joints, as you said, wrist, elbow, knee, but usually there is at least some distal or the small joints of the fingers involvement. I know ulcerative colitis and crohn have their own type of arthritis called 'seronegative arhtiritis associated to IBD', but the evidence of psoriasis and especially nail pitting on you may be the cause for the docs to diagnose you with psoriatic arhtritis. There are tests and clinical examinations which have to be done in addition to determine the exact type.
Also my advice is to pay attention to some infections that you may have acquired meanwhile which are possbile to cause you 'reactive arthritis'. I do tell this 'on duty' to everyone who is still undiagnosed, because I personaly still feel the bitterness of my bad experience with overlooked by the docs prostate infection for an year, which has caused my arhritis to appear.
Please visit rheumatologist as soon as possible and explain him/her exactly your symptoms.
about the exercises: Personally I don't beleive that exercises can affect positively an immune-mediated arthritis. May be a good lifestyle at all, but not specifically exercises. Personally I used to live the healthies life, ate only quality food, was running 4 km every morning and that was right before to feel my first joint pain ever in my life. So it did not helped to me. Even the opposite, if I was naive I could think that exactly this brought me the arthritis;) But the truth is that: how could I knew that I had prostate infection only by kind of 'simple penis rash' for a kind of small amount of time like 1 year.... ;))) Doctors should know that...;) so my advice is first to rule out infections. My opinion is that in any new case of arthritis in the world, the first thing that must be done is extensive rulling out of any possible known infections, even completely unsymptomatic ones, which could be chlamydia, HIV, tuberculosis .... Every other chronic diagnosis before to make sure that thare is no underlying infection and prescriping directly immune-suppresants is a CRIME!
sorry for my sharp tongue
http://arthritis.about.com/od/pa/p/psoriatic_arth.htm
Good luck, keep in touch