I have much the same problem. I thought there was physically something wrong with me, but all my blood work came out normal. I am going to look into supplements. So far B complex helped in the past and the occasional cup of coffee seems to help
OP, I don't know your background or if it is anything like mine, but I wanted to share some of my thoughts about my own experience, maybe some of it will resonate with you.
I am in my mid 20's, my entire childhood was continuously stressful. I went to go live in another state on my own and shortly after married an emotionally abusive man, then had two kids within 2 years. Point here is that the majority of my life, I have been under continuous stress. I have had my times, but generally for the last several years I don't feel consciously anxious or depressed. I am often happy, have a good mood and am optimistic. But under the surface so much of my life has been just having to get through the current situation that I haven't had time to process it all. Physiologically it makes sense that if the body is under constant stress when ever it feels able, it will shut down, try to recoup. Emotionally/mentally speaking I feel like I need a lot of time to just process things and zone out. Or even on some level it could be trying to escape reality. And I have noticed for me, if I feel overwhelmed, I shut down. Does it sound like something similar may be at play with you? I don't know what the solution is, but as they say, often times realizing where the problem lies is the first step.
Things to try: journaling, getting outside, exercise, supplements, starting simple routines to build some momentum, counseling/medication?
I hope you find something that helps.