Psoriasis Support Group
Psoriasis is an immune-mediated disease which affects the skin and joints. When it affects the skin it commonly appears as red scaly elevated patches called plaques. Psoriasis plaques frequently occur on the elbows and knees, but can affect any area of skin including the scalp and genital area. Psoriasis can also cause inflammation of the joints. This is known as...
I don't know if your psoriasis would necessarily make you more likely to get other illnesses, but it does sound as if your immunity is low.
I would go to your GP and request some blood tests as you may have some sort of deficiency.
Eat healthy and take a vitamnin supplement - I find they give me a boost and I have (so far) avoided getting coughs and colds from everyone else.