lots of tears

Hey, my DS is 14 weeks old and has always been a really calm baby who only really cried when hungry, this last week he's a different child. He cries so much, he's gone from sleeping full nights to waking constantly and just seems so unhappy all the time. I know babies cry etc I'm literally just curious as to why the sudden change in behaviour. I'm trying so many different things to make him happy and fix whatever it might be but nothing's working. He doesn't have wind and his gums don't seem to be bothering him. I think me and my partner have slept a total of 2/3 hours a night for the past week. Any advice would be amazing, thank you 😀 (also started spitting milk up a lot which he's never done before, it practically dripping out his mouth every minute of the day)