Lyme Disease a low B vitamin count, thyroid problems and Fibromyalgia can all cause problems with memory. However, it is extremely rare, but possible to have alzheimers younger than 30 - I did know someone at a message board I used to go to that had it at 26, but I repeat, it's extremely rare!!
Talk to your doctor, have all the tests run that you possibly can. The only true way to know if it's Alzheimers is to rule out the rest
Best of luck to you!