You sound a lot like me! I stopped going out a lot when I got my anxiety and I didn't exercise cuz I was too scared to. I'm getting a lot better now and so will you!
Your arm and leg are aching because they're not being used, my legs used to hurt terribly when I wasn't exercising. Sounds like a mixture of tension too and maybe just sitting wrong for a long amount of time! You should go to the doctor so he can tell you there's not anything wrong and maybe offer you help for your anxiety.
If you want to get more exercise but don't feel ready to go out the house yet have you got a Wii or a Kinect? If not you can buy exercise DVDs that are a good workout too! You can get a really good workout and not even have to leave your bedroom if you don't want to. They're pretty cheap too, I bought one of my exercise DVDs for about a tenner years ago!
xx