What Is The Treatment For Psoriasis?

I am a physician,aged 53 Yr, 172 cm, Wt=85kg, diabetic with hypertension for almost 2.5 yrs on Sitagliptin, Metformin, rosuvastatin, Fenofibrate, and olmesartan. Sitagliptin has been initiated for almost 2 yrs. The HbA1C=6.2%, Fasting Sugar 111mg% and PPBS 140 mg% with normal metabolic and renal profile. Iwas a known case of Psoriasis for 20 yr+ not on and systemic therapy. Since 1 yr I have developed severe prurigo nodularis with lichenification and trophis changes with near normalization of psoriasis. Intense pruritus is incapacitating and taking a toll on my sleep and professional discharge of duty. Can Sitagliptin be the cause, what should I do?