We all forget things. That doesn't mean we have Alzheimer's disease. Well, you can always go for a checkup. Normally there is nothing to worry about. A GP can always give you a referral if you are concerned.
Clinical diagnosis is the best approach.
Definitive clinical diagnosis of Alzheimer's disease is not possible. Other diseases may also cause related dementias. Surf through Alzheimer Web. There is a lot here. If you follow all the links you will undoubtedly learn some things that even your doctor may not know.