I find it interesting that you told us the whole story of your life. Not a lot of people do that and it's good reading that make me think at something else than medications while i read this. Being shy myself i can relate.
Now on the technical side of thing Citalopram belongs to a class of drugs known as selective serotonin reuptake inhibitors (SSRIs). Citalopram is used to treat the symptoms of major depression, social anxiety disorder, panic disorder and OCD.
If this medication worked for you for a long time and you like it why would you want to change medicine?
There is another class of drug you could try if you really want to try something else and it's the serotonin-norepinephrine reuptake inhibitors (SNRIs) they a class of antidepressant drugs used in the treatment of major depression and other mood disorders. They are also used to treat anxiety disorders, obsessive-compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), chronic neuropathic pain, fibromyalgia syndrome (FMS). You could try Duloxetine (Cymbalta, Yentreve) and see how it goes. But i really don't know why you would change medication if everything is okay with your current med...
Maybe you could jus gradually stop taking anti-depressant and control any panic attack or heavy anxiety with the use of some benzodiazepines like Xanax, Bromazepam or Ativan when neeeded untill you feel safe enough to quit.
There are many natural solution to treat anxiety too. Have you ever considered physical activity?
Physical activity is crucial to the body, it will make you produces a lot of hormones that are essential for proper body and mind operations. You can google hormones related to physical activity and their benefits and how crucial it is by yourself since i can't write it all in this post since it would be too long.
Also a healthy diet is really important and its even more important if you are active since your body will need more raw materials to make the industry work as the demand increase if you know what i mean.
You could also consider talk therapy and luminotherapy. Luminotherapy means light therapy and usually involves half-hour sessions in front of a bright lamp (10 000 lux), specially adapted to treat seasonal depression. The principle is simple: light exposure slows down melatonin production, fighting sleepiness and depression. The light reaches the brain through the retina of the eye, as nerve impulses, to alter hormone levels, which in turn reset your body clock and boost your immune system. Some doctors and health farms offer luminotherapy as a treatment, but there are also special lamps on the market for home use.
Anyway i am not a doctor and if you have concern about your medication, switching medication or anything, talk with you doctor and also tell him if you wan't to engage into physical activity if it's safe for you or if you have any cardiac trouble.
SNRIs act upon and increase the levels of two neurotransmitters in the brain that are known to play an important part in mood, these being serotonin and norepinephrine. This can be contrasted with the more widely-used selective serotonin reuptake inhibitors (SSRIs) which act more selectively on serotonin.