Gaining weight issues?

Anyone knowhat could be the cause to my LO not gaining enough weight?

My meals are typically 2 a day, breakfast and dinner and snack on fruit, oat bars and sometimes small meals like a sandwich in between. I limit my caffeine intake now, be lucky to even get 2 cups of tea a day🤣

But at birth my girl was 6lbs 8oz (38w and 5 days) at 3 weeks she was 7lbs 2oz, 6 weeks she was 7lb 14oz and at 8 weeks and 6 days was 8lbs 7oz and today at 9weeks and 2 days 8lbs 8oz.

She went from the 25th centile down to between 0.4th and 2nd so nearly dropped to the lowest. I EBF bur today been recommended by the doctors to do formula top ups (which I wholeheartedly do not want to do!!) She has plenty of wet nappies and poops every 2 days

In the day my LO feeds for 10-20 minuets every hour or two. In the night it's every 2-4 hours (her big sleep is from 2am to 6am)

What could be the reasons? She's alert and doing what she should at 2 months but we now have the problem that she's not gaining enough weight.