How exactly can I determine if I have Alzheimer's disease?

You won't be able to determine that for yourself. Even fully trained neurologists need do several tests and they generally order a PET scan, as well.

There are many things that can mimic Alzheimer's, such as medication reactions and un-known infections, which can be handled if they are caught early. Please see a doctor so that you can find out for sure. If you are diagnosed with Alzheimer's, there are medications that can ward off the decline for quite some time. It's good to find out exactly where you stand medically, as there are things that an help.
Carol