Hi SF! Welcome to Anxiety Zone...
Feeling jittery and shaky is a very common side effect of Celexa (Citalopram), so there is a very good chance that it is the anti-depressant. It could also be a combination of the Celexa, and you anxiety.
I am also on Celexa. I was started on it some 10 weeks ago, and I take 20 mg.
SF, do you have a physician that is starting and stopping your anti-depressant, or is this something that you are doing on your own? I have several reasons for asking this question. Normally, with someone suffering with anxiety (GAD), it is best to start an anti-depressant at a sub-therapeutic dose, and titrate up. Celexa is normally started at 10 mg, sometimes even 5, and then the dose is slowly increased every 7-10 days. I have never heard of anyone starting at 30 mg.
Also, it is not a good idea to be starting and stopping anti-depressants. When you do that, a higher dose may be necessary to get the same result as the first time, and there is an increased likelihood of the med not working at all. According to one study, the odds of anti-depressants working drops by about 20% each time you start and stop them. And this applies to all antidepressants, not just the one you have previously taken.
If you feel that your problem with anxiety (GAD) is a chronic condition, you should consider being on an anti-depressant indefinitely. This is something you should discuss with your physician.
The very best to you, SF!... Chuck