I know it’s an obvious thing to ask but has he had a hearing check?
Why is he not listening? Does he have problems looking at you in the eye? Or is he too energetic so he doesn’t stop and listen? Or is he demand avoidant?
Does he listen when he is doing something he likes?
Could you get a basic check up from gp to see if anything obvious is being missed? Sometimes they can offer pointers to support groups for early years parenting.
You mention MH. How is your mental health op? Should you mention that to gp too? If you are having constant broken nights it can really wear you down. Also, you can’t parent effectively if you are anxious or depressed and there’s no shame in asking for help. We all need it occasionally.
Fwiw, if it’s any consolation, I remember feeling exactly as you do about whether I was being too strict, or too lenient or whatever. Most parents do. It shows you are a good parent if you care. Bad parents are not in to self reflection usually.
You do need to work on confidence in yourself though if you can as the best parenting lesson we can give our dc is “example, example, example”. SEN or other issues aside, if you work on yourself, the rest will usually follow.