I think it will take a few days for the drugs to work. The absolute best thing to increase your supply is frequent feeding - how much you express is not a good indication of supply as many women have trouble getting much out with a pump and yet their babies do ok. So try as much as you can to get him on the breast.
Try not to feel bad - it's all trial and error in the early days and you will sort this out. The first rule is always feed the baby, so if you're doing that you're doing well
Illness might affect supplyl if you're dehydrated, but otherwise it shouldn't have much of an effect.