If you are already doing speech therapy and OT, go back to your doctor and ask for more suggestions or more testing. Seeing an ENT to check his ears was a great idea if you haven't already. You can also try a chiropractor and/or cranio sacral massage therapy (with or without telling your regular doctor). For both of these things you need someone who sees lots of young kids and is very gentle. My 3 kids and I see Melissa Shelton in Plano for chiropractic, and I love Ken Piercy for cranio-sacral massage (www.kenpiercy.com). When the PT/OT evaluator suggested we try cranio for my 5 year old, I rolled my eyes. 6 months of little or no progress in OT, and I was ready to try anything...including cranio. It turned out to be amazing for her. Everyone reacts differently, but you know after one massage if your child benefits or not. In the world of long-term OT and speech therapy, this is a refreshing concept. In my book, it's worth $100 and an hour to find out if this could be a helpful piece of your puzzle. You stay with your child the whole time, reading books or playing with toys while the therapist works with the child VERY gently.
Trust your instincts. If you think there is something wrong or something that needs more help than he's already getting, you are probably right - even if your pediatrician tries to blow it off. Don't disregard your gut. Your child is counting on you to speak for him. No one knows your child better than you.
Good luck,
S.