Decrease in supply...help!

Marlisa • I'm 31 years old & married. My husband and I had one miscarriage in 2008 and then had our daughter June 2009 and our son October 2016.
My son is 4 months old. I feel like I can't keep up with his feeding needs. I work full time so I pump at work, usually once in the morning and once in the afternoon. I nurse him before work and in the evenings /nights. I haven't been pumping as much as I used to. I tried the mother's milk tea and that didn't seem to do anything. I was told fenugreek tablets would be better then the tea? I've been drinking as much water as possible. I still take my prenatal vitamins. I tried lactation cookies. Any other suggestions? I really don't want to supplement with formula but I know I have to if he doesn't have enough breast milk. I just want to make sure I try everything I can.