I would probably agree with your dr.
My dh had a bout of stomach problems a year ago and at the time I was going through horrid panic/anxiety and depression. I was calling him home from work everyday in a real state and he was stressed up to his eyeballs. Not to mention the fact that he is the only one working.
His Dr said it could be IBS but tbh I'm sure its stress related.
I know myself when I get anxious and worried my stomach goes to pot (literally).
Tiredness is a symptom of stress/anxiety/depression too.
Give the Citalopram a go.
It normally takes about 4 weeks for you to feel the effects.