Breast milk and pumping help

So i had my son three weeks ago I tried my hardest to breastfeed but he just wouldn't latch no matter what I did. I had two lactation specialist try to help me but no luck so I started pumping that way he still gets my breast milk. I was disappointed that I couldn't breast feed but I tried my best. I've been pumping, but I'm losing my milk supply. At first I would get 4oz with both breasts and now with both I can't even get half an ounce.. How can I boost my supply???