LR not saving photo edits

I'm new to LR, I've been working with it for a few months. At first everything was great, but the past few times I've used it, it doesn't save my edits. I'll pull up a handful of photos to edit, make a bunch of edits to a photo, then go to the next one to edit it, and the edits on the previous photo disappear. I'm using version 3.4. I've tried un-installing and re-installing but that didn't work. Any ideas?