Battery, Alternator or Starter issue?

ShockWave

So about 10 months ago in January my car won't start. I jumped the battery and it starts right up. Then like a week later same thing happens again..the car won't start. So I figure I had a dead battery. Took the car to Autozone and they tested the battery and alternator. They said battery and alternator is runner good! But I have to jump the car every other week because it won't start. So I went and got a new battery and everything is fine for 10 months. Then today my car didn't start again. I to jump it and it starts right up. Took it to Autozone again for a test. The guy said that my battery and alternator is good.
I told him about the issues and he said it might be my starter. If its the starter then why did my car starts right up when I jumped the battery? If its the starter then the car wouldn't start at all. Also the car was fine for 10 months with a new battery. What do you guys think?