one trouble with pumping is that it doesnt stimulate your breasts and milk production the way that your baby does.
so one bit of advice i can give you is to nurse your child every time he wants - on demand. even if he is not actually getting much (because a little will always be there) the actual process of him sucking will stimulate more milk production, in fact, it is REQUIRED. supply increases with demand. if this means you have to nurse at night too, then thats ok.
this also means that you should never give your baby a bottle when you are present. it doesnt sound like you are doing this, thats good, but i know its easy for a pumping mom to do. this way you can have the milk you pump for times when you arent around.
when you pump, that milk has 24 hours that it can be consumed or frozen. however you are working this out, freeze any leftovers after the first 24 hrs, and build yourself up a store of milk in the freezer. on weekends im assuming that you are not pumping, but nursing only, and that is what you should do, like i said, his sucking will be better at stimulating more supply.
drink lots of water, relax and rest when you can, dont exersize too strenuously, if you are working out, perhaps back off a few days. ive heard mixed reviews of different things moms can take to increase demand, so i dont know if they work or not.
one thing that will affect your supply, (and actually, your let down process) is stressing out about your supply, or anything else. though a bit of a slowdown is normal as your baby ages and relies more on solid foods, you should try to avoid stressing too much over it. relax - listen to recording of your baby while pumping, especially if you can catch a recording of him fussing to nurse, or actually nursing. this will bring those nursing related sounds to you in a way that might help your letdown. perhaps close your eyes while pumping so you can visualize nursing! :D
contact a local or nearby la leche league. they helped me tremendously, and they can help you too! :D
good luck!