Artsy,
Here is a list of treatments -I’d be suprised if you tried all of them:
Treatments for more advanced psoriasis include narrow-band UVB light, psoralen with UVA light retinoids (eg, isotretinoin [Accutane], acitretin [Soriatane]), methotrexate (particularly for arthritis), cyclosporine (Neoral, Sandimmune), infliximab (Remicade), etanercept (Enbrel), adalimumab (Humira), and alefacept (Amevive).