I am 48. Over the last one year or so I notice that my ejaculation (i.e. the stuff that comes out in ejaculation...sperm ? seminal fluid? or just semen? I don't know the correct term) has become colourless, watery, very small in quantity and very thin i.e. Not the milky, thick, large in quantity and viscous sticky stuff that it used to be. I masterbate 2 to 3 times a week.
At the beginning, the stuff used to be lightly chalky without the thickness but lately it has become almost like water.

Is it something to do with men's menopause ?
Please advise.

Could be a prostate problem, as that is the gland that secretes a good portion of the semen volume, and its fluid is what gives the semen that thick whitish color.