Tweeking: A combination of two words, two and week. When you have been on meth (cranking in the old days) and up for two weeks you have a tendency to talk funny and slur your words. After two weeks when you try to tell someone what your problem is all you can say is "I tweek..." After coming down for a day before your next trip you realize that you said tweek and also realize that it is not only a homonym with tweak, which means to bend or force out of shape, but it can also be synonymous. And since you were very bent you think it is funny and go get an eightball, and your again tweeking in no time at all. This is the origin of the word, believe me I was there.
Moral of the Story: Don't do drugs
Pleeezzzze hlp ma, I tweeeeeeek blaaargghhh *thump*
In the next day or two after your regain consciousness you say; "Man I was tweeking."