3 month old has stopped sleeping through the night?

If he wants to sleep later and wake up later then you should wake him up earlier. Try setting your clock and getting him up at 7:30 and letting him nap every 2 - 3 hours. Decrease his afternoon/evening naps so he'll feel more tired come his bedtime. When my son was 3 months old he didn't even have a 5 hour stretch lol , you're luckier then you think!