Getting off the coffee and diet soda (or -ahem- any kind of soda) is a very good start. If you kick those, you will begin to hydrate yourself properly. Many times, headaches are the result of being systemically dehydrated.
( and of course, headaches = liver/gallbladder, and meds affect the liver in a bad way.
Wanna be inspired by Big Change? listen to Dave.
He got off several meds, lost a huge amount of weight, reversed diseases, literally saved his life... http://www.youtube.com/watch?hl=en&v=4f-xdUKt8Sg&gl=US
he didn't do a water fast, I don't think. But he juiced and stopped all meat, etc. All cooked food. You might not want to go that far. (raw) But raw, organic vegan IS a great way for sick people to get well.
In Natural Hygiene, (which promotes water fasting as one practice) it's all about being a "nutritarian". That is, high-density nutrients. Eating to live, not living to eat. Plant-based meals. Fruit and vegetables... less is more.
There is a huge protein myth out there: the body actually recycles its protein, and there is lots of protein in plant-based foods. Normally, we (in the west) get too MUCH protein. I'll let Chris address the issue of the meds and a water fast. You may have to work up to a water fast.
Anyway, welcome to a new way of living...One step at a time. Just in time for a new moon, too!