I've experienced a very similar situation. You felt utterly stuck and helpless. The truth is, the hardest part is to begin.

I started out small. Not working out, but stretching. Feeling my muscles. Doing some basic self care (making myself something good to eat, styling my hair, tending to my nails, etc).

And then, instead of being crippled by my self-consciousness, I decided to get angry. My anger actually helped me get over my shyness. I rationalized that alllllll of those people barely cared if I lived or died (and only if I was standing right in front of them). SO, why would I care what they thought about me? They don't matter. When you walk into a store, people don't care what you are doing there. So, when you first leave your house, go with a purpose/a mission. After you get some practice in, you feel so free. You'll never question whether or not you have to justify your presence to ANYONE. Meandering never felt so liberating. I know it sounds silly, but it worked for me.

It, also, helps if you are doing something for someone else. I don't know why, but it was always easier for me to get out of my comfort zone if it was in service for someone with greater needs than my own.