I feel like I am reading my own mind. This is EXACTLY the same issue I have had for sooo many years and I have no found any help or anyone else with this issue. Can you tell me please have you found any help yet, I realise this over 10 years old but I just stumbled across it now!
I've been suffering from the same pain as you. I think it started from a hit to the right side of my head at work. I've been to many Doctor's to, with no answers. The only thing that helps me is yoga, light swimming, and heat. For some reason cold does not help. As far as the severe constapation, I have to take metamusil every day. The only answer the doctor gave me is fybromialgia also. Its crazy you have the exact same symptoms as I do, right down to the twitching eye. Did you ever have a injury to the base of your neck or spine? Physio did help me to. I've had these symptoms for 12 years now.