I understand. The only time I really leave my house is to go to lectures (can't even manage that all of the time, however) now that I'm at university. Other than that, I pretty much stay inside the house 24/7. I'm currently on a four month summer break from university, and the only times I've gone anywhere have really only been in order to go to the supermarket or when I've absolutely had to go somewhere, certainly nothing voluntarily out of my comfort zone.
Oddly, in my early teenage years I would always try to get out as much as I could - I'd go around on buses, walk around in the evenings... all by myself (and, albeit, usually only once it was dark), but getting out nonetheless. Then, as I got older I would quite easily spend months indoors, or only venture out with my mum once a week for the food shopping. I wasn't happy about it, but I had just somehow lost that drive to force myself to go anywhere.
A big issue for me is that I have skin problems, and that really doesn't help with my agoraphobia. I think a lot of the time I would go outside just for the sake of it, but often I just don't feel up to being seen by anyone because of my appearance, so it's easier for me to just stay inside and avoid the world. I might attempt to 'get ready' by putting some makeup on in some feeble attempt to improve my appearance, but one look in the mirror and my mind will become set against any previous plans. I'll also often go to bed with the idea in mind of going out in the morning, but come the next day that just goes out the window as I just feel too anxious, and staying in doing nothing yet again becomes by far the more attractive option. However, this past week I've really become set on trying to push myself to at least leave the house 3 times a week, even if it's just walking to the high street and back. I just feel so depressed being cooped up all the time, yet it's so hard to actually change the routine.