There are also reasons that a mother might not be able to make enough because of something physically going on with her (some examples: PCOS, thyroid issues, hormonal reasons etc.) It's important to figure out if the challenges are happening because of your ability to make enough, your babies ability to remove enough, or a combination of both! (themilkmeg.com)
Coffee, excess cortisol, and even cortisol resistance are the most common hormonal reasons for slow metabolism in women. (saragottfriedmd.com)
More muscles lead to better insulin sensitivity but also reducing cortisol (If you don't exercise too long) so maybe hormonal reason is fine and also when we gain muscles its more lean body mass and BMR rise little bit...? (idmprogram.com)