Hello Jeff, and welcome to Anxiety Zone. My name is Chuck, and I am one of the Global Moderators here on the site.
I was started on 20 mg of Celexa (Citalopram), just over six months ago. One of the side effects that I had was indeed the "achy legs", just like you are experiencing. Mine too felt as if I had just had a strenuous workout on a bike, especially in the upper leg/thigh region. This is a start-up side effect, one of a number that I had. On day 16-17 into my treatment with Celexa, I had a dramatic reduction in my side effects, including the achy legs.
All side effects are gone now, and the Celexa has worked very well for me. I would say that I am somewhere between 90 and 100% better.
I hope that the Celexa works well for you too.
The very best to you, Jeff!... Chuck