Thank you for your advice and calming my nerves!
It's not cancer.
It could well be a thyroid issue. It can be many things. The fact it happens around menstruation is the key in seeing it is more than likely hormonal. The body retains fluid as the cycle goes along in the event of pregnancy it will keep that fluid.,Menstruation comes along and all that fluid is released. Some women pee more, some sweat more.
It wouldn't hurt to have your thyroid levels checked anyway. Many women have problems after a baby is born, and hyperthyroidism (no it's not cancer!) is notorious for sweating excessively.
Yes, it's probably hormones. Since I was never able to have children, I can't tell you if this kind of hormonal fluctuation is typical after birth. I have night sweats due to perimenopause. Black cohosh supplements put a big dent in them. If you're breast feeding you don't want to use anything that isn't doctor-approved, so give him/her a call and start feeling better.