Decreased milk supply HELP!

I've been exclusively breastfeeding my baby and pumping 3x while at work two days a week. The other 3 days I work from home and nurse her. At night she nurses around 8pm then 2pm and 5am then every 3 hours or so. Recently my frozen milk stashhas gotten low so I've started to pump during the days I'm at home also. However, most pumping session (10-20 minutes) I'm getting very little. Maybe 1 or 1.5oz. Even when pumping at work I've gotten very small amounts compared to what I used to get. I'm 4 months PP and worried my baby isn't getting enough (she's been nursing longer recently) and I won't be able to produce enough milk to give for her when I'm at work. HELP! How can I increase my supply and ensure she's getting enough?! I'd really like to continue exclusively with breastmilk.