That's seminal fluid without the semen. I get that every once in awhile when sleeping since HRT, and sometimes before that. This is caused by the multiple erections during the night while you are sleeping, normal prostate function. Keep it clean down there, this is also normal seepage in normal males as well and will supply the jock itch fungus (tinea cruris) with the fructose sugar. The fructose is added by the prostate during the normal ejaculation to charge up the sperm.
Joelene