Millions of women experience pelvic or other sexual health issues at some point during their lives. But there is no need to suffer in silence. The conditions are treatable and there are resources readily available to help. Fact: Pelvic health problems are not something that you just have to accept because you are a woman, have had children or have reached a certain age.
It is possible for women to urinate during sex. During sex, pressure can be put on the bladder by the penis, fingers, or another object. As a result, prodding the bladder in some way during sex is a relatively common occurrence. There is also some debate about whether female ejaculation is urine or another sort of fluid. Female ejaculation does not happen to all women, but some experience fluid coming from the urethra during orgasm.
Getting wet: discharge vs. cervical fluid vs. arousal fluid
I suppose you're sure it's not urine? In order to find out, you could collect some, and ask a nurse to test it for you. Many women do leak a little 'pee' during sex — but this is much commoner among those who have had children, and I note from your details that this does not apply to you. Either way, I don't think you've got anything to worry about. But if you'd like further reassurance, why not go and get yourself checked out by a doctor who is experienced in sexual matters — for instance, at a genitourinary medicine GUM or Family Planning Clinic.
You are in the throngs of great sex when all of a sudden there is a new sensation. It takes your brain, very occupied with other things, a few seconds to switch gears and process. And then you realize that you have inadvertently emptied your bladder. This is a real medical problem called coital incontinence. The exact number of women who have this condition is unknown as many are reluctant to talk about it.