fully breastfeeding

hi i'm a mom to 3½month old baby she is exclusively breastfed, latch all the way. her output is normal very good and also weight is good. and she is happy. but i just cant seem to pump anything. cause i thought of pumping some to keep on days i cant be with her for urgent matters. isit the breastpump or my milk supply is just enough for her to latch and not enough to pump#advicepls i tried pumping today after 2months of not pumping, i barely get 10ml. and also i tried mixed feeding, bought a small packet of formula milk on days my husband takes care of her. but she dont like the milk she wont drink, not sure if the bottle she dont like or the taste of the milk 😅