Pumping 😟

Hi I just bought a Breast Pump and I am not sure if it's me that doesn't know how to use it or I am not Producing enough milk!!... my LO is 6 weeks old and lashes on but seems to not get full, so I bought it. Now when I want to pump I don't even fill 1 ounce of her bottle 😢 it's getting me frustrated and sad to think I've been giving her nothing and that's why she cries sometimes and have to feed her formula. Any advice on what I am doing wrong please and thank you