“Watery discharge”

I think you have an infection. You need to visit the health clinic to be checked and treated.

This sounds most like a possible vaginal bacterial infection. You should see your GYN doctor to confirm and treat.

Vaginal discharge may or may not be related to a sexually transmitted infection, that would be the first thing to rule out. This would be done with a vaginal swab during a gynecological exam.
The odor if related to a classic fish odor may be related to bacterial vaginosis, which may or may not be related to sexual activity.
This would also be diagnosed at the time of gynecologic examination with a PCR (polymerase chain reaction) swab. Rare causes of a watery vaginal discharge could be a sign of fallopian tube cancer pelvic ultrasound could be done to evaluate this. If suspicious pelvic MRI would be even more helpful.

Usually it is residual discharge after your period. It should resolve in 3-5 days. If you use tampons, make sure all tampons are accounted for!
Seek help from your doctor/OBGyn if you have persistent discharge.
Take care!

A malodorous discharge likely signifies a vaginal infection more common after the menstrual cycle. Whenever you have an upset in the chemical composition of the vagina (pH balance) from douching, medication use, unprotected sex, bubble baths, etc, you change the balance between the normal healthy bacteria and unhealthy bacteria. You should have an evaluation to be checked and treated.