4 month sleep regression: what can I do?

My 3.5 month old has gone from a champion sleeper to a nightmare who wakes every 1-2 hours each night. We’re both exhausted.

Is this something he will figure out on his own? Do I need to do something?

I think he’s too young for sleep training. The only way to get him to sleep is lots of rocking and feeding. And around 4am I give up and hold him so we can both get some sleep.

Does this just go away like a phase or am I stuck with it until sleep training?