At 4.5 months, what you are describing sounds very much like the classic 4-month sleep regression, which is one of the most well-known ones because babies go through a real developmental shift in their sleep cycles around this age. The good news is that since he was already sleeping through before, there is a good chance he will find his way back to that once this phase passes, though it can take a few weeks. It could also be a growth spurt layered on top, since both can happen around the same time and the extra night feeds are his way of keeping up with demand. I would just ride it out for now and see if things settle on their own before worrying too much, lah.