Please help me...

So when my son was first born he fought me when I tried to breastfeed him. So he lost so much weight that we had to start formula (broke my heart) i felt so guilty that I couldn't breastfeed him.... i started pumping and alternating feedings with the milk I got. Sadly my suppy took a dump and now i only produce 20ml combined out of both breasts and he is almost a month old so its not enough... well tonight I thought "let me throw him on my tit just to see if he will latch now" and to my surprise he did! But now i have 2 problems.... 1- i dont make enough to feed him only with my breasts and 2- he is starting to pinch my nipple and it hurts like the dickens! Can anyone suggest things to try or help me with this?