What Causes Rashes On Back And Neck Post Intake Of Buprenorphine?

I have for the last two nights been taking Buprenorphine 200mcg sublingual tablets as well as Amitriptilin 10mg following a severe shoulder operation. I have this evening not yet taken any tablets but have developed a rash on on my back, neck and creeping up my face. No spots, just redness. Could this rash be caused by the tablets I took last night? Would it take that long to develop? Should I take nay more tonight?