Colic or no?

So I have a 3 week old baby and she's been feeding exclusively. However, on Thursday I started adding formula to the milk because I'm going to be going back to work at six weeks and that's what the doctor told me to do. On Saturday she started to be really fussy but it wasn't too bad. Now today, she has been screaming and crying all day. I don't know if she's gy because she hasn't had as many bm's as usual or if it's because of the formula. Also, I have been sick since Friday. It started with VERY bad stomach pains which I still have and I have been having very, very loose stools starting today. The stomach pains are so bad that it almost feels like I'm in labor! So, I don't know if she has maybe caught what I have and the diarreah hasn't started yet, or if it's gas, or if it's caused by the formula, or if she's just colicky? Any advice would be greatly appreciated!!