It’s very common for one breast to produce considerably more milk than the other. In fact, for 7 out of 10 women, it’s usually the right breast that is more productive!
This may or may not work but if you’re trying to even out production on both sides, you might try increasing stimulation/breast emptying in the lower producing breast by starting more feeds on that side, pumping more often on that side, power pumping, etc. You can also try hand expressing for a few minutes after every feed/pump session. Check out the Hand Expression highlight on Instagram for some great demo videos.
Some women have also had success with Lechita®. Lechita® contains a blend of organic ingredients designed to encourage the flow of breast milk. Fennel seed can optimize the quantity and quality of breast milk while other supporting herbs provide calming effects that may reduce stress and tension, prompting the milk letdown reflex. Anise and caraway are also traditionally used as digestive support for mom and baby. We can't guarantee that Lechita will turn your "dud" into a "stud" but it'll do its darnedest to try!
If these tips don't even out production, keep in mind that breasts are sisters, not twins so differences in output are completely normal!