Breast milk drying up

Pa

My LO is 8 months old and she has stopped nursing properly ever since she was 4 months old. The time for which she nursed kept reducing. She gets tired of sucking. And now it has come down to 2-3 mins. I hand express breast milk and give her with a spoon. Even that is not possible each time I feed her during the day as I'm always exhausted. I checked her weight 2-3 days back and realised that she had lost 1 kg 😔. I have started giving her formula from today. I want to be able to breast feed her at least till she is 1 and a half year old. Is there a way that I can boost my milk supply? I have started having oatmeal. Other than that is there something that I can do or is it time for my milk to dry up now? I only feel the first let down now. I'm not sure if the milk comes after the first let down. Please advise.

Also after feeding her for 2-3 mins, I am able to hand express only around 60 ml/2 oz from both the sides combined. Is that extremely less?