Pumping at work

help please! I am a photographer at a portrait studio so while I am at work I am pumping. my son is eating every 3 to 4 hours during the day and it's almost impossible with my work schedule to pump as much as I need to be. it's hard to get a break when were busy and I'm the only one there or there's only one other person. I keep going about 5 hours before I'm able to pump and because of it my milk supply dropped drastically and my son wasn't getting enoufh to eat. I've gotten it back up because I had a few days off and it still isn't back to where it should be. I don't know what to do. I'm afraid my milk is going to dry up or I'm going to dwindle so much that he has to keep supplementing with formula :( any advice?