I have image related websites with hundreds of pages each, every page gets indexed within a week. However only around 10 images are indexed in google images for all of my sites. It's been about 3 months btw since these sites have been launched. Does it seem like I might be doing something wrong or is this normal?
Wrong! Google will index an image without Alt-text just fine, scroll thru Google Images & you'll find plenty of images that don't include Alt-text. If your image has a keyword name (example: fast_cars.jpg), it will get indexed by Google, & show in the Google Images SERPs for those keywords.
This is pretty normal. If you want to index them faster increase the number of incoming links to your images. This way Google will better categorize your images as important and post them on the search engine sooner.
Yea you must not have read the other comments, the alt tag is not the problem. I'm guessing it's probably more of a link thing, I would imagine the more links going to lets say a pig site with the word pig in it would help more than a lot of other things. Along with relevant keywords on the page.