Doesn't sound like a growth spurt if DS isn't drinking more...
Are you feeding when he wakes at 3 hrs? How does he respond? Does he drink heavily then fall asleep or seems awake or in discomfort, etc...?
2 hr naps sound typical... or did you mean 2 hrs total? How many naps and what are the A times now?
As you probably already know, their sleep changes constantly, especially the first 4 months. Hopefully it's a case of riding it out and he'll revert to the long stretches, but looking ahead... there's a big gs at 3 and/or 4 mos along with developmental changes. Whatever is the case, practice independent sleep as much as you can.