I have only suffered from it occasionally and mildly. Counselling helped me immensely (it was for depression and the reasons for my depression, but had the knock on effect of helping with the agoraphobia too) Anti-depressants (citalopram) also helped. When my son was studying psychology for AS level he learnt that for the most part agoraphobia is more a fear of the people you may meet or the difficulties you may encounter whilst outside rather than being an actual fear of being outdoors. It was certainly true in my case and I found a very early morning walk before most people were up and about (summer time - not much use to you now lol) helped me realise that outdoors was OK . Then it was a case of coping with each thing as it happened. Sometimes I used to get home and close the curtains and shut the world out, but at least that was progress. I still don't like anyone other than family coming into the house. I have just stopped taking the anti-depressants and have regressed a little but it's early days yet.
As I said though mine was mild and I now know what caused it in the first place. Maybe your GP could help? (by phone) Mine was surprisingly helpful.