Help! Why has my 5 wk old started waking up more at night?

My 5 week old has slept through the night since birth. Since bringing him home from the hospital our schedule has been bedtime around 10-10:30 and he’d sleep until 4-5 then back to sleep until 9ish. The past two nights he’s been waking up at 1-1:30 then yesterday he was up almost hourly starting at 3 until 9. (It’s just now 1:30 and we’re feeding right now) I’m curious as to what could be causing him to have started this when nothing has changed in our routine to cause this. I’m a first time mom so any help or thoughts would be appreciated, thanks in advance!