Is my baby underweight?

My baby girl is 13 months old now and her weight is still 7.3kls. 5 months old clothes nya kasya pa rin sakanya..Worried ako that she may be underweight, super bilis nyang mag digest..30mins every meal sya kung mag poo poo..sometimes 4-6 times in daytime mag poo poo in small amounts..nagsusuka rin sya kapag naparami ang kain..any tips mga momsh how to increase her weight? Thanks in advance.. 1st time mom and super worried..pero super kulit naman ni baby and masigla despite the weight issue..