Whatever you do, do NOT stop taking it cold turkey. I once had a prescription for Citalopram, and I only took it for 3 months before I noticed the effects starting to wear down. Instead of doing the smart thing and simply upping my dose, I just quit taking it, and I felt terrible. It felt like temporary insanity; I was anxious as hell, and my mind was just bouncing off the walls. It could have been worse though, I've heard that some people who have gone off SSRIs cold turkey have even experienced psychosis.
Anyway, talk to your doctor, and see what they can do. Like I said earlier on, upping your dose is probably not a bad idea if it worked for you before, as the human body tends to develop a tolerance to certain substances, mainly drugs, when consumed on a regular basis, and this tolerance can prevent smaller amounts of these drugs from doing what they need to do. If Citalopram has done NOTHING for you at all, then ask to switch to a different medication.
For the record, I am not a doctor, and I am not a lawyer, and any medical advice you read online or hear from anyone who isn't a doctor should be taken with a grain of salt.