Milk production reducing, advice needed

Sarah • :)
I breastfed my first till he turned 2 years. My second is 9 weeks and she has been doing great with brestfeeding she weighed 13.1 lbs on her 8 weeks checkup. I went back to work about 2 weeks ago and been pumping since she was 4 weeks. In the past 2 weeks my milk production has reduced a lot, i barely make enough! I'm eating properly, taking my vitamins and pumping or feeding her regularley. Any advice is welcome. Thanks