Why do I want to isolate myself?

So ever since a couple years ago I dreaded going out with family and the slightest mention of spending a night over their houses will literally make me cry (they are like strangers to me even though I visit them every year) and puts me in a bigger state of sadness. I hate going outside in general, shopping for food, clothing, etc etc. makes me so mad and I can’t stand it. But why? As a kid i’d do anything but now all I want to do is stay on the internet or not even on the internet, just inside. I don’t have many friends to go out with and nor do I even want to go anywhere with them I always distance myself. I also do have depression but on the days I feel ok I never want to go anywhere, am I just really lazy?? I have no idea anymore all I know is that I hate being with people even though everyone around me loves interacting and the outdoors. I wish I was like that. (Plus having social anxiety doesn’t help me. over this summer I realized I’m not eating correctly, my muscles ache from not getting out of bed, I can’t sleep properly)
Just in case this was really confusing i’ll ask my question(s)
Why do I want to isolate myself so much?
also is it just because I’m lazy?