Usually bacteria. There are normally a number of different bacteria and yeast present in the vagina. Over 70% of women have gardnerella vaginalis in the vagina. The different bacteria keep each other in check and the vagina typically has a benign odor. When one bacteria overgrows (especially g. Vaginalis) a foul odor can occur. Other reasons for an odor are infections (pid), yeast, and foreign body (lost tampon).
Vagina smell. The first possible reason is a bacterial, abnormal ph, check fwith your gynecologist, pap smear, sc, others.
Bacterial vaginosis? The most frequent cause of strong vaginal odor is bacterial vaginosis, an overgrowth of mostly normal bacteria. BV odor typically is fishy, as you have noticed, and sometimes there is increased discharge. Trichomonas and other STDs are more common in BV, so have an STD check. This should be easy to diagnose and treat; see your doctor soon. Good luck!
Bv? Change in vaginal ph could create a foul smell which could mean bacterial vaginosis. See your doctor for a pelvic exam.
Secretions. Depending on any chemicals used during sex (lubricants, etc) the smell is most likely just a "stirring" of the smells inside the vagina along with any ejaculate that may be present. Semen has a "smell" unto itself. If using a condom, they have their odor. If you are having a foul or offensive odor, perhaps you have a bacterial vaginosis. A fishy odor is usually bv. Get checked and get treated.
Bacterial vaginosis? The main cause of strong vaginal odor is bacterial vaginosis, an overgrowth of mostly normal bacteria. Typically the odor is fishy, but odor is very subjective and one person's "maple syrup" may be another's "fishy". Sometimes there is increased discharge. Trichomonas causes similar odor, and other STDs like gonorrhea or chlamydia are more common in BV. See a doctor soon to check it out.
Possible BV. One of the common vaginal infections that women can get is BV or bacterial vaginosis. One of the symptoms is a vaginal discharge with a fishy odor. An exam will be able to tell if you have an infection.