Not Pregnant, On Period, & Nipple Secretion?

[Confused]

I'm 32 and started a new relationship. Recently had sex, 4 days into my menstrual cycle, with my boyfriend who told me afterward that my nipples secreted a tiny bit of fluid after he played and sucked on them.

In all my years of being sexually active, I have never been told this has happened by any partner. In my previous relationship, which spanned about 10 years, this never happened. I asked my ex if he recalled this ever happening and failed to mention it?🤔 (we're on good terms and after 10 years, quite comfortable with being direct no matter the topic). My ex told me this never happened to his knowledge.

I tried to google this, and apparently "it's normal for women in their reproductive years to secrete fluid sometimes". The articles I came across also said that prolactin fluctuations are normal during the menstrual cycle which may cause lactation. However, my boyfriend told me the fluid was colorless and tasted mildly bitter. It was not the typical description o the internet for such an occurrence... the added element of it happening only during sex and when he sucked on them may also be something to note...

I guess my question is, has this happened to anyone else and it was not a result of pregnancy, cancer, or pituitary tumor? and did it continue to happen or did it stop?