In hearing your explanation of shaking of the lips, I agree with Kent that it may be an endurance problem, but of course, like going to the dentist - it's nearly impossible to diagnose your problem "over the phone." If it IS an endurance problem, Kent is correct - long tones with slow changes in dynamics can work wonders.
I've had this problem myself at times when I haven't played my oboe for awhile. For me and like most oboists, we try to keep our embouchure as relaxed as possible. When I'm out of shape, after only a little while of playing - either I catch myself biting down (NO! NO! NO!) or my lips sometimes quiver and occasionally my tone.
Like a great athlete, double reed players especially, should think of themselves as long distance runners. How wonderful to feel we can just play and play without feeling like we're dying! . This just doesn't happen overnight and won't work quickly - like cramming for an exam.
Oh, yes - and Kent mentioned your reed. Try playing on a REALLY easy reed for awhile and see if the problem works itself out. You may just need this break - mentally AND physically. I think I had this problem too - reeds too hard caused this problem.
I'm sure you'll figure it out, Dear. *PLEASE* report back to us and let us know what you've discovered, if you're still having problems, and/or how things are going.