MM,
Call your Neuro in the am, ASAP. Get a visit with him or at least get him on the phone. You should not be in that much pain and misery. It could be T.N., Trigeminal Neuralgia of the whole side of the head/face. Or migraine, or a virus. Do you relapse? Perhaps that is it.

Only your doctor can tell for sure. If you can't see your Neuro for some reason get to your PCP or the ER. Benadryl is dehydrating and can cause constipation too. I am not sure about the other drugs you are on. Do you have a fever? Your shot was after this so do you get flu-like from the Rebif?

So many answers you need to find out what is wrong and get it treated. Good luck to you and I hope you feel better soon.

Maybe you feel you need the ER now. Do you?