One of the secrets of happy people are to have a 'purpose' - whether this is a vocation, a project or a hobby. Something that makes you feel alive, that gives you that 'hell, yeah!' feeling. The problem is finding it.... but once you do, you'll know. What kind of things interest you? Are there any hobbies perhaps ? I have a busy job but have just started Ceroc classes and am absolutely loving it, a friend has started classes in watercolours. Charity work is always good when you're feeling up to it, perhaps there's something that isn't as pressurised as helping out in the shops? Dog walking for a animal home can benefit them and you, as you get fresh air and fun too. When you do feel a little better, it's worth checking out Meetup.com for any local groups - there's bound to be something you can join that would make your days more fun.
Another important element in being happy is 'community' and this is why so many forums like this exist. Please do try getting out and about and finding that community that gives you the lift you need.... Dog walking again is one that is sociable and fun; could you perhaps arrange a weekly get together with old friends over a cake and tea; or get involved in some interest group that you've always fancied.
The third point that I find important for me is 'achievement'. I hate being unproductive and feel so much better when I've had a day where I've achieved something, or got closer to the finish line on a project. Make a list of things you need / want to do and try ticking some off each day, this puts you in the right frame of mind for the rest of the day, and possibly will give you the strength to venture out.
YouTube is fabulous for a lift when you're feeling at a loose end - there are so many motivational videos on there that really inspire you and give you the get up and go to make change. I'd highly recommend Jack Canfield, he's like everyone's favourite grandad and so very wise but easy to listen to.
If you're finding it difficult to get motivated for anything and anxiety is taking over, I'd suggest chatting to your doctor as there may be medical reasons you've lost your mojo.
Hope it all picks up for you.,
GG x