Dopamine has been proven to help short term memory processing. Estrogen triggers a release of dopamine. Women can improve performance by 10% on complicated mental tasks during ovulation when estrogen levels peak, and nosedive the two weeks after ovulation.
Some women have naturally high dopamine levels, and ovulation puts them over the top in dopamine and impairs their thinking.
Caffeine also triggers the release of dopamine, which can be detrimental for some women at certain times of their cycle.
Extra estrogen applied to men seems to have no significant effect.
What should you do? Start monitoring your schedule. Mark down when you feel most efficient in mental tasks, whether it is your work, or focusing and concentrating on reading or other tasks. Once you know when you are most optimal within your cycle, take care not to take in caffeine or other stimulants when you are peaking - save them for your down times. Monitor how well you do and over time you'll have your own custom formula for optimizing your focus and concentration.