3 month old advice please!

My baby is now just almost 3 months old. She has been a pretty easy baby until the last two weeks. Prior to, she was only getting up once a night and we even had a couple 8 hour stretches in the crib... We switched her to the crib at 2 months. She had also been eating 3oz of formula every 2.5-3 hours with longer stretches at night. The last two weeks all of a sudden she's waking up all night and WILL NOT nap! She's so tired but when we try to put her to sleep she fights it and screams. Not to mention I can't put her down without being a ninja-she cannot know you're putting her down or forget it. She eat every two hours now during the day and when I tried to give her more than 3oz to try and make it longer stretches, she still wants to eat every two hours. When she is awake and alert she is a happy baby but she keeps getting so cranky because I know she is so tired. 30 min catnaps are the longest she'll do during the day! I'm worried about taking her to a babysitter next month!! Any advice?