12 week old suddenly unhappy all day but fine at night

[Mumof3cheeky]

Ds4 has been great until 3 weeks ago when he suddenly wouldn’t settle to sleep and reduce his feed by half. He still sleeps well at night but daytime is draining. He would take 3-4 oz then scream when I offer him more and get himself into state then pretty scream up until he falls asleep for 30min then again would only take 3-4 oz and the circle continues. He is very big boy born 10punds and used to take 6-7 oz every 3-4 hrs. However I’m not sure he is lacking the food otherwsise he would be up feeding at night but just can’t get him back into a happy daytime boy. Changed his teat to 3 month as well but no change
We think he is also teething but wouldn’t explain the not eating bit and again the nighttime sleep
I’m frazzled
Any suggestion appreciated

My son was exactly the same and is just starting to come out of it (he's 16 weeks now). I think there's a growth-spurt at 12ish weeks which can make baby eat more/ eat less/ fuss more etc.

Do you refer to The Wonder Weeks? Also a useful guide (although I know some disagree) about developmental changes in babies that affects their behaviour. There's an APP if you're interested...

That sounds promisinf thank you. I used to use Gina ford but couldn’t see anything referring to this one in the book so will definitely have a look at Wonder weeks. Thanks again x