when you say can't keep food down i'm not sure if it is forceful vomiting or frequent spit up. gastro-esophageal reflux (ger when food comes back up is common in babies occurring in half of babies under 6 months old. some are referred to as "happy spitters" meaning they frequently regurgitate (2 or more times per day) but are growing and eating without other issues. but if it gets worse with time or is more projectile or is accompanied by other symptoms (wheezing gagging etc. ) and there is poor growth it's a problem. gastro-esophageal reflux disease (gerd) is ger coupled with problematic symptoms and needs a doctor's attention. if you suspect your child has gerd or some other problem see your doctor again. for more on gerd see this webmd article. you also might want to see a lactation consutant for tips on breastfeeding positions and feeding techniques (like pumping before feeds) to decrease spitting up after feeding. good luck!
i have 2 month old that has had issues with keeping breast milk and now formula down have done everything doctors say