Not producing enough!!

Deissy
My son will be 4 months on the 28th and I'm currently breastfeeding and giving him formula as well I want to eventually stop the formula and go back to strictly breast milk but with working 3rd shift and not having much time to pump at work it's getting really hard to keep up my milk supply with his feedings. Any moms out there ever had this problem and tried something that actually worked? I need help!