How to use data generator for regression keras?
When you are using a pre-trained model, you should use it's specific pre-processing function,
Below is an example for resnet50.
from keras.applications.resnet50 import preprocess_input
train_datagen = ImageDataGenerator(#rescale = 1./255
                                    preprocessing_function=preprocess_input)

Always display/print your image/label for a sanity check.
You may use the below snippet.
#Quick check the DataGenerator

import matplotlib.pyplot as plt
for image, label in train_generator:
    plt.imshow(image[0])
    print(label[0])
    break;