Are there any other non-mental health problems like low iron that could explain why I am slow?
Do you feel normal in your day-to-day life or is there anything you struggle with?
Say if you had to carry two bags of groceries up a staircase, would you be OK or find it difficult?
If you feel healthy the issue is most likely your training. You need to be patient. Set goals that are achievable and work on those.
Maybe some different goals would, be good. Maybe you are getting stale. What about trying the 800m? You could do time trials. I find the 800m is a good one because it is somehow a lot easier to do an 800m time trial alone than a 1500m or longer.