There is an app called the wonder weeks and it gives you an idea based on your baby’s due date, when the next leap it will be, play time ideas, the phase they will be in (fussy, happy). It’s like 15£/year. I found it quite interesting to learn more about what they go thru at certain times
I was told that it could be the 4 month sleep regression. Babies transition into sleep cycles away from the newborn sleep. They are also able to see more and are developing new skills so often get over stimulated and over tired causing issues with sleep. My little one is the same and this is what I was told. Hope that helps to reassure you :)
It is likely to be a growth spurt/leap at that age. The first big regression is around 6 months/16 weeks. I would try increase the formula by an oz through the day and see if that helps, if not it’ll be a case of just having to ride it out by the sounds of things x