Sudden grump

My once happy, sweet, hardly ever mad baby is now all of a sudden an all day grumpy pants. And she's taking like 5 naps a day but still sleeps amazing at night. Is this that 4 month thing? She's about to be 15 weeks old. I can barely get her to play with toys or do anything fun because she's either tired, hungry, or just extremely fussy. I hope it's just a growing thing and not her actual personality coming through haha she doesn't seem sick but she was never like this before...she rarely used to cry and was just happy to be here 🤷‍♀️