Your pediatrician is not usaully the best resource when you have concerns like this, and you should never "wait and see" or assume that everything will work out later when it comes to such serious developmental issues.
I would suggest that you contact your local children's hospital and find a Developmental Pediatrican and have a full evaluation. This is the very best thing that you can do for him, because a Developmental Pediatrician will miss nothing, and you will get every kind of referal that you need, from speech and langauge, to occupational therapy, to neurology; all these different professionals will contribute to the comprehensive evaluation and you will know exactly what is going on and have a plan for intervention that you can trust.
You have described some classic presentations, do not ignore it, and no matter what anyone says about thier "cousins best freind's nephew who was just like this and is now a brain surgon," do not assume that your son's outcome will be so rosey unless you seek and follow standard medical treatment and therapy for a real medical issue.
Also, there is no evidence that suppliments or diet make any real difference in developmental issues. You may be able to improve his general health with vitamins and diet, but you will neither reverse, cure (or cause) a neurodevelopmental disorder with diet or "natural" supliments, so don't beat yourself up with any thought that you have been feeding him wrong, or letting him have dyes or sugar; these are myths perpetuated on a population that is desperate to find an answer that they have some control over.
Make the appointment today, it may take many months to get in. In the mean time, one thing that you can do with him is to be concrete. Instead of saying that he does not listen, say that he did not respond to what you told him. To him, "listen" means hear, not comply. Say only what you mean, and put it in active tense for him. Tell him what to do instead of what to stop doing and avoid "don't" statements. Say "hold your body still" instead of "stop moving around." Fewer words are best, and getting his physical attention is going to help you communicate with him.
Last, don't fall into the trap of thinking that because he can pay attention some times, he does not have a problem or that it is within his control at other times and he is just to lazy to work at it. This is a vicious circle that will put you at odds with your son and damage your relationship with him. Put kidney desease in place of ADHD and you will kick yourself for ever assuming this. "my son can keep from wetting his pants sometimes, so he must not have kidney desease" it sounds outragous. Praise him when he can pay attention. It does not surprise me that he can pay attention when he can either hyperfocus or when he is at his very best (in the morning when he is rested.) This behavior only means that there is hope for him with proper treatement, not that he is able to control the behavior in other circumstances.
You might want to reduce the sensory overload, and unitl you have his evaluation, keep him in more quiet surroundings and avoid over the top, stimulating, crowded gatherings.
Make the appointment, stay consistent, get his physical attention before you speak to him, reward and praise him for good behavior, use active statements "what to do" statements, and reduce his sensory overload.