I’m going through something similar (also 9 weeks). She went from 6 hour stretch down to 4-4.5 hour. She also kept waking up as well. Didn’t seem fussy (though week 8 was crazy with her fussiness) but really hard to put down to sleep
Your son may not be getting enough to eat during the night or he could be going through sleep regression. You could try and feed him more or give him gripe water and see if he's just gassy that might help.
It may be that he’s learning a new skill which is keeping him up, this is often the case when they regress. Is he sleeping a good amount during the day?
Thank you all for the responses! I’ve just accepted that it must be either a growth spurt or developing a new skill. It’s nice to have validation that I’m not the only one😅
Unfortunately I’m not experiencing this, but only thing I can think of if it’s another growth spurt? Is he wanting to feed at that often too? I hear that this stuff is common at 3s,6s, and 9s (in days, weeks, and months).