Hi there,
certainly anxiety and or depression can cause an array of mental and physical symptoms, and is commonly the cause when there are several symptoms that have no other explanation. Also, anxiety/depression can amplify pain that may be present from other things (ie make you more sensitive to pain).
It is easy to let symptoms go and explain them away as anxiety, so I would always make sure that your issues are investigated in a reasonable way if they are persistent. Your back pain may be made worse by anxiety, but because it responded to injections, it is unlikely due to anxiety alone. Also, pain that wakes you at night can be worrisome, so make sure your doctor knows that is happening, although it may be that the problem is that you aren't sleeping well due to the anxiety/depression, and are feeling the pain because you are awake, rather than the actual pain waking you up.
Also, make sure he/she knows about your stomach issues, and that other causes have been ruled out.
I think the Celexa is a good idea, to see if it makes a difference. The side effects usually subside within a few weeks, and can take up to 6 weeks to make a difference, so try to be patient If it is not tolerable due to side effects, talk to your doctor about trying something else, as there are other medications that maybe won't bother you as much.
Good luck.
JMK MD