Could be infectious but considering the antibiotic course completed it is ruled out. Next is CMPA, Celiac disease or infectious colitis.
Next Steps
for CMPA - try daily elimination for 2-4 weeks and see if symptoms get better.
Extensively hydrolysed formulae or amino acid formulae. will work as dairy alternative.
For other diagnosis exclusions need consulting with pediatrician
Health Tips
keep an eye on growth, height and weight as malabsorption can lead to nutritional deficiencies and as a result cause poor growth.