Hi, and thanks for your question
While it’s not possible to diagnose what is going on over the internet it sounds very much like you may have something called Bacterial Vaginosis (BV).
BV is not a sexually transmitted infection (STI) but rather an imbalance of the healthy bacteria that normally lives in the vagina. When these bacteria get out of balance, symptoms can occur. These symptoms are commonly described as a fishy odor and an increased amount of watery, thin vaginal discharge (You didn’t specify in your question, but I am assuming that you are a person with a vagina. If I have gotten that wrong, please forgive the assumption).
BV can be very easily treated with a 1-week course of an antibiotic called metronidazole. You can visit any walk-in clinic or sexual health clinic for assessment, diagnosis and treatment. I would recommend a full STI screen for HIV, syphilis, chlamydia and gonorrhea as well as testing for BV as sometimes STIs can also cause these symptoms.
Let us know if this does not answer your question or if you have any more questions or concerns.