Adhd meds don‘t work that well during your premenstrual phase because your estrogen is lower and estrogen lessens severity of adhd symptoms a bit - so your adhd symptoms are more severe in the time leading up to your menstruation, so the same dosage of meds doesn’t have the same effectiveness. Might be that you have more accurate self-perception due to the meds and thus notice better how hard exactly adhd affects you during that phase in comparison to the rest of the cycle.
You might want to talk to a doc about whether it could be smart to temporarily increase your dosage of meds during your PMS each month.
I myself have such strong PMS and other hormonal issues (hyperandrogenemia due to a defect in the ovaries) that I just take my pill without break (after my endocrinologist’s and gynaecologist’s advice) and also have an additional hormonal medication for the hyperandrogenemia to block it. It’s both helped with both the PMS and the adhd, especially the estrogen-heavy combined pill that I take without break, but the classical pill or other hormonal contraceptives might not be for you if you don‘t want to/can’t use hormonal contraceptives.