As someone who deals with doctors on a daily basis, I can tell you that I have the same problem!! When I want to tell them about my concerns for a patient they don't listen to me half the time. I feel I do get some respect over other, younger nurses on my unit do to my age (translation: experience) but it all comes down to the fact that they feel they know more than you do, and they are applying their knowledge base to you. In other words, they are applying their general knowledge to your specific case. Also, doctors are usually only interested in the reason for the visit. If you go in for a sinus infection, they do not want to hear about your stomach pains.
Believe me, I'm not saying it's right, just explaining the situation. The approach I try personally is to say, "I know you're the expert here, but I'm the expert of ME and this is what I'm experiencing."
If you continue to have issues with this doctor, it's time to find another. A good doctor-patient relationship is as hard to find as a good spouse and just as important!