Exclusive pumping

De

My son is 5 1/2 months old and I exclusively pump with occasional formula supplements. I’ve noticed recently that my supply is decreasing. I haven’t change my water intake I still eat oatmeal every morning with flax seeds. I have been back to work since 8 weeks and haven’t had a problem til now. So my question is what can I do at almost 6 months to increase my supply?