Milk Supply!

I was doing so well breastfeeding. I went in Tuesday to have a few wisdom teeth extracted and was put on hydrocodone for the pain & decided to pump and dump instead of breastfeeding. I was giving my baby formula and he wouldn't drink it and felt very warm so I took him to the Emergency room and was told his tummy doesn't like the formula so continue to breastfeed, but my milk supply seems to be drying out due to stress I'm assuming. What can I do to up my supply? Just yesterday morning I pumped 5oz bottles. Today I was unable to pump an ounce using both sides.