Ramping down is probably giving you withdrawal symptoms. They shouldn't last more than a week. Painkillers will help, but if you're trying to get away from caffeine, make sure they aren't in your painkillers, too. A number of extra strength painkillers have 50 mg caffeine (Excedrin has caffeine). Of course, everyone is different, even ignoring how ADHD interacts with caffeine, so no one solution is perfect.
As someone who has maintained a consistently low caffeine addiction for decades, these are important factors. I keep it low so it isn't required to function normally and I still get a kick with reasonable results when I need it. And I like the taste of Coca-Cola.
Are you sure it's the caffeine? I ask because I have no problems at all with caffeine, but coffee in any real quantity, eg. more than in a Coffee Crisp or coffee cake, gives me stomach cramps, but I can take a 200 mg tablet on an empty stomach and have no problems at all.
Everyone's different, and I'm curious if this is another of those.