5 weeks old baby constipated?

I have 5 weeks old doughter which cries all day , for few days we are using gripe water and seems to be better .. untill today , she is constipated and didn't poop for 2,5 days. She gets red , moves her legs and cryes 2-3 hours after milk( formula feeding) She is cinstipated , I tried with stomach masage , fennel tea , hot water but nothing helps. If anyone has idea what should I do..... I am mixing gripe water with formula. Is it better to give her before feeding , mixing or after feeding?