not enough breast milk

My LO is 6 months. Since the beginning I haven't had much milk, it took forever to come in also. Over the past month is has decreased a lot. My LO eats (3-4 hours) but I hardly have any, By the next feeding I'm just as empty as when he last ate. Im never full. Now it's gotten to the point where it doesn't even build up over night! Yes I've tried drinking plenty of water, pumping more, teas and brewers yeast. Any idea what's going on or some tips? TIA