No weight gain 😞

Ria

My lo is 5 days short of 6months.. exclusively breastfed.. and started with fruit and veg purées , but he hasn’t significantly gained weight.. he is just 14.3 lbs but birth weights is 8lbs, am sure this is less. I don’t have appointment til 30th June , so need your suggestions! Should I start to supplement formula ? If so , which brand can I use ?

Tia