Well... based on the fact I am old (so I know something of what that feels like) I'd say first get yourself checked out medically (assuming you haven't already.) And if there's nothing going on medically then, if you're not already receiving mental health services (I sort-of suspect you probably are... but just in case), I'd suggest making arrangements to do so. If you're struggling with depression, you're psychotic & agoraphobic I would think mental health services would be vital. (If you're already receiving services, & they're not helping, maybe you need to find different services?)

I also happen to know something about not going anywhere but being in your house. You wrote you've been doing that for 4 years. One thing I know is that the longer a person spends hold-up at home the more difficult it is to be out in public. And so given that, although you feel old you're actually still young, I would think it would be important to see if you can find a therapist who is skilled in helping people who have agoraphobia.

Here are links to 2 articles, from Psych Central's archives, on the subject of treatment for agoraphobia. The second link is to an "Ask the Therapist" column where the writer asked about getting help as a homebound person. The writer's circumstances may be different from yours. But I think the therapist's reply is apropos:

The High Price of Your Untreated Agoraphobia | Don't Call Me Crazy

How Does a Homebound Agoraphobic Get Help? - Ask the Therapist

The bottom line here, at least from my perspective, is that you've fallen into a pit, so to speak (of depression, psychosis & agoraphobia.) And it's going to take time & a lot of work with skilled mental health professionals for you to get back to being the young adult you actually are. I hope you are able to find the inner strength to make that happen.