Constipated 5 Week Old

Am
For the last week my poor baby girl has been very constipated. When it first happened and she hadn’t gone in 48 hours I did the rectal temperature trick and it worked right away. Then she didn’t go for another 48 and it didn’t work so we took her to her pediatrician and she said to put 3 tsp of Karo syrup in each of her bottles. She said she should go after 3 tsp but to keep giving it to her to clean her out. 21 tsp later she hasn’t gone. Doc just said to keep giving it to her. She is so miserable and is pushing and grunting 24/7. We’ve done tummy massages and bicycle kicks constantly. I feel so bad for her. Any advice? Also she is formula fed (not by choice) but has always been on the same formula so I don’t think that’s the issue and neither does the pediatrician... Just want my baby girl to feel better!