Sorry to hear this Lissielou.
My DH has also been diagnosed with psoriatic arthritis. He saw a consultant regularly for about 2.5 yrs but last month, he got signed off and doesn't have to go back unless things get worse again so it isn't all doom and gloom. I think it is an unpredictable disease but at the moment he is lucky.
However, at the beginning he was given medication which helped a little (he noticed when he didn't take it) but had to stop as he only has one kidney and it can be quite harmful to kidneys unfortunately.
Instead he has had several steroid injections into his joints which lasted about 3 or 4 months and which worked better than taking tablets. It wasn't very pleasant to have done, especially the shoulder one, but it was worth it.
He is not symptom free and is very stiff when he gets out of bed, had trouble if he has to use a keyboard for too long. He is managing it at the moment by taking supplements. He takes rosehip capsules, cod liver oil, glucosamine and a multivitamin. He hasn't had a proper cold since he has been taking them!!! He notices if he doesn't take these for a day or two as well so they must be having an effect.
The rosehip he started taking after reading a recent study of people with RA which came from Denmark I think. Apparently it is quite effective so might be worth a go.
DH still drinks orange juice but I think citrus fruits can have a detrimental effect on joints (my mother has it too and avoids it) Can't think at the moment of other dietary restrictions but I am sure there are some.