Baby weight

Hello moshies!!! My baby girl is 8 months old but since 6 months hindi sya masyado nag gain ng weight. She weighs only 6.8kg per her last check up last Nov. pero we noticed humaba ang height nya. Her pedia told us na ok lang daw as long as active baby which is true kasi super likot nya. But Im still worried kasi kung kelan nag start na sya mag solid saka prang ndi nag gain. Is this normal kaya? Na experience nyo dn ba ito with your babies? Btw, we change her formula milk from similac tummiecare to Nan Optipro HW.