using unsupervised learning algorithms on images
Have you included dropout in your model? It can help avoid overfitting issue. 

For your problem, yes, you can use auto-encoders, GAN, etc. for feature learning.
However, I'm not sure if unsupervised learning can help, since it's more like a training issue. Your have label with your data so supervised learning is ideal, plus supervised learning generally shows better performance than unsupervised in image classification. You might want to check the false classification examples in your dataset, and try to alter the CNN structure based on that, which would be a more direct way.