Unfortunately, diagnosis of ADHD is not an exact science. There is no one sure test to make an absolute judgment about the presence or absence of the condition. Diagnosis is particularly challenging when viewing young children. Youngsters mature at different rates and there is a range of what might be considered "normal." Normal differences in temperament, personality, and energy level may lead some to label a child as ADHD when he is merely immature or just exuberant. That said, however, a clinician with a strong background in normal development as well as ADHD can help to tease out whether your child fits the criteria and might need some direct intervention at this point.
And no, all young children diagnosed with ADHD do not have to be medicated. Many times a behavioral intervention plan monitored by a professional may have a significant impact. If your pediatrician is not willing to give you a referral for an evaluation for ADHD, try contacting Children and Adults with Attention Deficit Disorders (CHADD) at 1-800-233-4050. This parent advocacy group has branches throughout the country and is an excellent resource for parents and professionals. They should be able to help you to make a connection with a professional who can give you some guidance and support. Some branches even sponsor parent education groups that can help you to learn new strategies for coping with your child's behavior. Equally important, they will give you an opportunity to share concerns and ideas with other parents who are in the same situation as you. You might also want to read Dr. Larry Silver's Advice to Parents on ADHD. This is an excellent resource for guiding parents to handle behavior problems.
You are right to try to get a handle on your child's needs while he is still very young. Early intervention can help to make your child's adjustment to kindergarten a smoother one. Good luck!