Just seen this thread and i thought I'd add my own experiences.
Citalopram - I found to be quite an ineffective drug, it didn't dent my depression at all. Different drugs suit different people. At the depths of my depression I was on 90mg Mirtazapine, 15mg Diazepam and 75mg of Venlafaxine all in a day, spread over the day of course. I'm now down to just 45mg of Mirtazapine in the evenings only.
Depression is environmental as well as chemical. I would suggest seeing your doctor once maybe twice a week to discuss how the drug/dosage is affecting you and discuss it indepth. Different drugs over different timespans or combinations of drugs are there to help and adjust the chemical.
Fingers crossed, you have a good GP, I went through four at my surgery, until by accident, I saw the head of the practice and he took it upon himself to book me regular bi-weekly appointments. After four months of trying to see Psych Services, he rang me one afternoon to tell me that he'd got me an appointment in two hours time. Sadly, I had to say no to it 'cos I had to collect DD's from school. I then got a letter from Psych Services saying in 5 days they'd close the case because I hadn't seen them. Well! a busy London borough, NHS Psych Services are exceptionally overloaded. I would have loved to get advice and help from a professional but my GP has done sterling service.
Be aware of your environment and the triggers for depression, yesterday because of the tube strike, the awful weather and the kids not being able to go to/get to school. I was thrown into quite a black mood - I alleviated by taking them swimming, it tired them out, they enjoyed it, they fell asleep early giving me a break.
I still have a prescription for diazepam but only to be used on as "as needed" basis (that was advice from my doctor). My" as needed" is when DW starts drinking heavily in the evening and starts difficult to understand drunk rambling conversations, I take the Diazepam in conjunction with the Mirtazapine to send me off to sleep quickly and deeply. Not good, but her drinking is one of my triggers to send me into the blackest of humours.
Another effect of depression, is the loafing around it causes, I've had to seriously force myself to do stuff. I've lost 2 stone since October when I was diagnosed with depression, in the main by watching what I eat and walking places. It was evident even to myself that in the run up to the diagnosis I was comfort eating and being indolent. In March I plan to start running in the evenings with my eldest DD in an effort to get us both mobile and a bit fitter.
There is no set timespan to depression, I'm ambivalent with the one day at a time approach, I was like that at first and I could see that I couldn't keep living like that. Take one day then turn it into three days at a time, then one week, start to grow your vision of when thing will become manageable over longer periods of time. In December I started to set myself small weekly achievable goals, I found this book [http://www.amazon.co.uk/Sketchnote-Handbook-Illustrated-Visual-Taking-ebook/dp/B00E981K1W/ref=sr_1_1?ie=UTF8&qid=1391683866&sr=8-1&keywords=sketchnotes Sketchnotes] invaluable. The methodology of sketching notes, plans, ideas, and goals, fitted well with the jumble of thoughts that appear at random to spring into my head.
Part of my depression was caused by financial problems, working at devising a coherent plan to solve it and making small tangible inroads via weekly goals has helped no end. Its helped me to take control of the situation and the environment (which wasn't helped by DW calling me a control-freak last night - I've never been a controlling person which, part in parcel, has been one of the environmental factors for my depression).
My last point is be aware of the effects that depression has on your nearest and dearest. Especially the circular, I'm depressed, it make DW and the DD's react in a certain way, I react to their reaction causing a spiral of events that aren't good for anyone. Again that's something I can take control of (by using Vogon poetry and Vulcan (TOS) logic), by seeing it as triggers and knee jerks.
I think I'm on the road now to recovery, my doctor has advised that I don't have to see him for a month to see how it goes.
So after all that, my summary is this, know you have depression and start to take control of it. Control the chemical - in consultation with your doctor. Control the environment - understand the triggers and cause and effect it has on you.