My DS1 has ADHD. I was in labour with him for 7.5hrs from first contraction.

He was posterior and was born with forceps. He was distressed and spent 12 hrs in the SCU.

Like MD, too often wondered of the lack of oxygen when being born may have contributed to the issues he's had.
I think that when there is something wrong with our babies we as mums automatically become hard on ourselves. Try to be gentle on yourself hun. Your DS's ADHD is certainly not your fault.
Sending huge hugs your way