Breastfeeding after the fact

Ok so my son will be a month old on wednesday. I switched to formula when he was 4 days old. I regret it so much but I had to. So I've noticed that my breasts still leak a little bit it's mostly clear. My question is would I still be able to pump at this late stage? Would I even produce milk if I started now? I really want to be able to give him breast milk. If not I definitely want to try again when ever I have another. Thank you.