Aiyooo, switching back and forth memang boleh trigger tummy issues gitu, baby's system dah adjust to breastfeeding, so going back to formula sometimes causes reaction. A few of us mums in my circle also went through this, and honestly kena try a different formula brand atau maybe a gentler one like HiPP or S-26 Gold, since Enfalac might be too heavy for baby now. But since baby dah vomit and diarrhea, better check with your paediatrician first to make sure nothing else going on, could be intolerance, could be the timing of feeding. How long dah baby experience this? Maybe also try increasing breastfeeding sessions first if possible, before introducing formula again.