Is this really Caffeine withdrawal or could it be something else?

Sounds like you had the same liquid diet that my husband has. He has just recently traded in his mt dews for gatoraide and poweraide. He has been complaining a lot about headaches and some body pains and we have decided it has to be the lack of caffiene in his system. His headache tends to go away if he drinks a couple of sodas with caffiene in them. He has never gone 3 weeks without caffiene. I don't think he is able to.