So confused :(

Took my nearly 5 month old ebf to get weighed today, she d only put on 2oz in 3 weeks (at 21 weeks she now weighs 10lb 12 oz- has always been small though and between 2nd and 0.4 percentile) The two health visitors told me to start solids to give her a helping hand with weight. Im so confused because the same health visitors told me last month never to start solids until 6 months. Also been told babies dont need calories from food until 8 months- its just for fun. Why am i now being told to give her food at 5 months and they are obviously expecting her to get calories (and put on weight) from it? Im kinda heart broken as wanted to ebf until 6 months like reccomended. What are yr experiences?