Too late?

Is it still possible to increase supply at 4 months PP? I am currently breastfeeding but I feel like I barely have enough to go by (and my son would totally drink more I think, if I had more, and maybe would sleep better at night...) and I wish I would have a little stored too, but when I try to pump after a feeding or between feedings, I can barely get out 1 oz from both breasts (either by electric, manual pump or hand expressing) I am drinking water, eating, resting, tried oatmeal, teas, currently taking fennel pills...what am I not doing?

Thanks in advance!