OOO forgot to mention the dehydration factor. The loss of water in body tissues. If you are dehydrated you can do a test yourself. Pull the skin on your forearm up and let it fall back on its own. If the skin drops back slowly you are dehydrated, if not you may still be dehydrated but not as much. It sounds like you should have had an IV. Your electrolytes maybe out of wack and you are dehydrated. Try Gatoraide also..
3 weeks is unheard of for not having a bowel movement I think. Better still get more advice from your doctor and insist your concerns and state it has been 3 weeks with no bowel movement. Wow..again..just suggesting what I would do....Hope it helps I can feel your pain.

Carol CG to Husband age 60 Stage IV SCC right tonsil T4AN2B tx rad x 35 chemo x 2 Currently after treatment no sign of cancer in throat. (all clear to date)