Hi Sue,
Citalopram, as well as other ADs do not have an immediate effect on anxiety. They are different from benzos which calm you down as soon as you take the pill. ADs work on the serotonin levels and build up over time to increase your sense of wellbeing, thus reducing anxiety symptoms in the long run. I wouldn't expect to calm down overnight when taking just two doses of the AD. There are also side effects that are different for different people, in the initial few weeks. Some Drs prescribe other medication for these initial few days to help with the side effects and to decrease anxiety until serotonin builds up.
My advice would be to persist at least a week or so to see the effect of the AD. You may also discuss with your GP for other medication to help you through this period.
Good luck!
Milamam