Image Sizes

Hey everyone, I seem to be having an issue with the new Photos app. My iPhoto library is 19.69GB however my Photos library is 17.26GB. I now have images that show up as 179KB instead of 3.5MB like they did in iPhoto. Also all the images I have of my newborn son are have been reduced in image size. This really doesn't make sense to me and I need help on this as soon as possible as I didn't do a time machine backup before the update!