Baby is 9 weeks and supply dipped

Is it normal to have dips in supply? I've been breastfeeding only when I'm home and pumping while I'm working. I've noticed I not feel let down anymore and my breasts aren't feeling full like they normally do. I'm a week and I half into my birth control which is the mini pill. I'm trying to pump at least three times at work I work eight hour days til my breasts are empty. I'm used to pumping any where from 20 to 30 oz while at work. And id like to keep that type of supply up any ideas?