Feel like I'm on the verge of burnout

Hi!

I feel like I am on the verge of burnout, although I'm not sure what that really is as I'm still learning what I struggle with, how my autism affects me etc (24 yr old, female, diagnosed in 2021).

I work full-time, social media copywriter, this is my first job after graduating uni in 2020 (freelanced over covid, some part time temp work too) and I've been here almost 3 years. 

I have this constant exhaustion at the moment, I feel so tired when I finish work, physically, mentally, emotionally... 

I also have this feeling like I'm not doing good enough, but I know these are my own pressures I put on myself, and that I need to keep going and doing better, which obviously doesn't help.

Other issues I'm seeing is that I'm regressing a lot - things I have always been able to do are becoming a lot harder and I'm finding difficult to do. This includes coming up with decent meals for lunch, talking to people, and doing things independently. 

I have this other feeling of being disillusioned with work that's creeping up on me. Where I work is small, only 5 of us there, we all get on well, super supportive especially of my support needs, they've said I am always welcome here as long as I want AKA I will never be out of a job. 

The issue is I'm vastly underpaid, and they know it. I brought it up in my review and they acknowledged that I deserve a pay rise (and am due one), but until new business comes in they can't give me one. 

Looking for a new job is an option (as my family have said), but I am in such a good position here and I cannot face leaving and the job search process again for the sake of my mental health. 

I feel like this burnout coming on is fuelled by this feeling of "work is work" and feels like a grind on the basis of being underpaid. But I feel wrong for feeling that way...

Do I sound crazy?

Any tips for getting over these feelings/dealing with burnout?