I agree, express those lumps out.... she's only 4 weeks old, so your supply is still hormone driven & I imagine might take a bit longer to dry up than if she were older. You might need to wean a bit more slowly, to be a bit easier on your breasts?
I don't know how long or often you are pumping, but reducing the duration of your pumps & only doing it when needed should see it gradually ease.

FWIW when I weaned my first (at 1 week old) I was told not to express or touch my breasts at all...baaaaad advice I spent days & days sitting on the toilet with a warm towel wrapped around them, while they dripped into a bucket. Oh boy, I would not do it that way again definitely pump it will be easier on you.