Some cognitive decline as we age is considered normal, but there are certain symptoms that are not see commonly and are considered more characteristic of Alzheimer's disease. Short-term memory loss is perhaps the most well-known symptom of Alzheimer's disease. There may also be problems expressing thoughts (such as being able to find the right word, as you mentioned) or comprehending requests, and/or confusion or disorientation to person, place and time, among other symptoms. What is important to note, however, is that these are also symptoms of other dementias and other medical and psychiatric disorders, some of which may be treatable. To best determine the cause of your symptoms, a comprehensive examination by your physician is recommended.
You cannot tell if it is dementia just by knowing that you forget. There are many types of dementia. You could have dementia or other medical issues. Please check with your GP and ask for referral to a neurologist or psychiatrist to do memory test to find out what is wrong. A GP does not work on memory issue.