Look like sth wrong is in your pipeline. If you have > 50k images, over-fitting with Dropout should not be a big problem.
Try pretrained model and learn just last layer (so dont optimize rest of them, just pass model.fc.parameters() to optimizer)
If this also doesn’t help, maybe make again random split between training and validation images (maybe distribution of images in this two sets is too different)
Last part is training without Data-Augmentation, maybe turn it off and see what will happend.