Why do I feel so hollow and sad all the time?

I can give a lot of the credit to switching to online school and not being as social as I used to but nowadays no matter what I do I just feel like there is a pit in my chest. Before I was able to go to the gym or play video games and I would get distracted from it and feel fine but now even when I do that I still have the same feeling. I want to see a therapist or psychiatrist or whatever but nobody in my area is accepting new patients.