It's not unusual for the SSRIs to pocket a month to start having an effect. Good for you for sticking beside it long enough to catch there. A lot of nation get discouraged rash and will give up after merely a few days or a couple of weeks. The most important entry you can do now is stick beside it. Hopefully you will continue to discern better here over the next few weeks. Above adjectives, if it is helping, stick with it. If you get the impression better down the road remember it is the medication that is helping you and don't merely quit all at once.
As to the physiology aft why it takes so long, I'm not really sure. The best I can donate you is that nobody probably really knows. Citalopram works by decreasing the breakdown of serotonin (a "quality good" neurotransmitter for lack of a better track of putting it) in your brain. Moreof it stays within the synapse where it does its charge and this hopefully helps you to surface better. Some people simply take longer to respond to these increased level than others.
what jason said