I'm not completely sure on the bruises, but it is very common for little ones to get a rash a couple of days after a fever. Maybe just the body reacting to the fever??? I would def. keep an eye on it and maybe even give the dr. a call! Good luck!
It might not actually be bruising, it might just be the rash fading. My daughters both broke out in some weird hive like rash last summer, and after it started to go away, they both looked like abuse victims for a few days. It's definitely worth keeping an eye on, and maybe go ahead and call his doctor, just to have him looked over.