Quoting Boob Tick's Mom ebft.: What makes you think your supply is low?
Regardless of how often or how long I let Owen bf, he still screams like he is starving to death. The other morning he bf'd for nearly 30 minutes on one side. I was super excited and thought I'd just been imagining everything, but the second he unlatched, he started screaming. I offered the other breast and after no more than 2 minutes of super hard sucking he was unlatched and reaching for the other side. It became a back and forth of that for the next hour or more, and he would just scream and scream. SO finally insisted on offering a bottle, and he ate more than 8oz in 5 minutes.
We haven't been to the dr for a weight check lately (he's just over 3mos), but my at-home guesstimates (weigh myself, then weight myself holding him) haven't changed at all in over a week, when he has been gaining close to a lb a week. He's a big boy and a big eater.
I always pump when I come home from work, as I was engorged after a shift. Now, no longer engorged after work, and I'm only pumping maybe an oz from each side as opposed to the 5-6 I used to get.
I know there are a few more reasons, but I'm tired right now! Sorry! Hope that's enough info to help at least.