Is my baby gaining enough?!😩

Baby girl was born July 21st so was 4 weeks old exactly yesterday! She was born at 7lb10oz, and dropped to 7lb4oz by day five. By day ten, she had gone above and beyond her birth weight and weighed 7lb13oz although the scales could have been slightly out. We weighed her yesterday and she weighed exactly 9lb, so from her birth weight, she's only gained 1lb6oz in 4 weeks.. Is this normal??!!?! I see all these other babies born around the same time and weight who at 4 weeks are nearly 10/11lb.. I exclusively breast feed by the way, she poos and wees enough too and I feed on demand so she she's constantly feeding! Any comments please?🎀