Classifying Car Data By Year
I want to say how I solved my problem for anyone who is looking for a similar question. 

My categorization was a mistake. I realized later that, I gave the same photos to my model and waited for the different results. For example, I had nearly same photos in Audi A3 Hatchback/5 2009 and Audi A3 Hatchback/5 2010. When the model starts training, first it learns data. Then it predicts and validates output itself. If the output is wrong, it tries a different way to success. But wait a minute, there was no mistake. I gave you the same photos and waited for different results! My categorization failed here. 

I categorized my cars by body changes like Audi A3 Hatchback 2008-2013. Except for categories that have the wrong photos, my results are great for now. 

Now, we will work on better photos and better year categorization.