Why Is My New Born Infant Vomiting After Breastfeeding Since Starting Taxim-O And Gastica For Fever And Gastric Issues?

Hi my baby is 21 days old earlier she was having fever doctor gave T-98 but the she used to get fever again after 5 hours and temperature was not coming down below 99.5 so doctow gave Taxim-o she also have gastric issue so doctor gave Gastica but yesterday onwards everytime I am breastfeed her she vomits..please suggest