Hi Querida,
I worked with a mother years ago who experienced similar symptoms with her
baby whenever she had her menstrual cycle.  Actually, when her baby nursed it
would throw up if she was on her period.  Plus the baby really cut back on
feeds during this time.  After this going on for several months we did much
investigating and research and found that when moms are on their menstrual
cycle the supply might decrease slightly.  But more importantly the milk
supply tends to have a higher level of sodium while moms on on their periods.
Some babies are very sensitive to this change.  Some moms notice a salty
flavor to their breastmilk then.  This mom increased her fluid intake when she
was on her periods in hopes that it would help.  It's similar to weaning milk,
(being higher in sodium), and this flavor tends to cause the baby to request
feeds less frequently.  A few days after her cycle ended her supply would
boost again only to start over next month.  I hope this info helps.  Warmly,
Sue