Pumping After 4 weeks

My son was born with a tongue-tie and my milk production was poor. He was introduced to the bottle on day 1 due to low blood sugar. Even after he got his tongue-tie fixed we had a lot of latching issues, it also didn't help I didn't produce enough for him to be satisfied. I was a mess, I fell into depression and gave up on it and went with formula. My son has been having a lot of digestive problems. After yesterday's visit to the ER the pediatrician suggested pumping. I told her I gave up on it since when I did pump I only got .5 oz combined. She pretty much told Me, something is better than nothing. I do leak 2 x a day. And upon stimulation I can squeeze some out. But I feel lost as to when to even start. I know diet is important and I do have a manual pump and that's about it. Everything else, I'm clueless about. Help?!