What Causes Itchy Body Rashes After Taking Otezla?

I was recently diagnosed with psoriatic arthritis & started taking Otezla about 3 weeks ago. In the past week-10 days, I have developed large areas of rashes that itch horribly. The areas of the bumps do not resemble the psoriasis I have experienced for years on the palms of my hands but instead, are larger bumps almost like a mosquito bite but cover a large area underneath my upper arms & my right thigh-even the insides of my ears itch! I am not on any other new medication & I have not used new soap, laundry detergent, etc. Could these itchy areas be a side effect of the Otezla or a huge outbreak of more psoriasis? I can t get back into dermatologist for 10 days. Any suggestions from anyone & would taking benadryl be ok? I have been using the cream & ointment the Dr prescribed but neither really helps with itching or clearing the rash areas. Thank you for any suggestions!