Trying to increase milk supply.

First of all is 4 weeks PP too late to try and increase my supply? My baby is getting enough but I would like to pump and freeze as well as nurse him. That way when I'm done letting him nurse and wean him from the boob, he can still have my milk. I want to build up a freezer stockpile of breast milk! I am already trying to nurse my baby more, and was wondering what other things I can try. Over the counter first. If nothing else works I will go to my OB. But for the moment I would like to try and do this without my doctors help. Any advice is appreciated! Thanks ladies!