Agree fully with the former post - get the diagnosis and help.
My son is extremely bright but had great difficulty with executive functioning. It was/is much more serious than your situation. Everything for him was a challenge, even with meds, accommodation, and therapy.
He had a LOT of trouble in high school, and yes it greatly affected his confidence. But he worked his way through it, and I’m glad to say he is now in grad school and doing well. It’s still not easy, but time has definitely helped.
My best advice, looking back, is to understand that he is facing challenges that other kids do not, and he needs your support. We questioned our son about things that I now regret very much. And when we talk about it now, I can tell it still hurts him very much that we often didn’t believe him. If I could do it over, I would make sure I backed him up more.