What can cause a slightly odered brownish vaginal discharge, but no itching..?

Several things: This symptom could still be a vaginal infection. Itching is not always necessary. You will need to see a clinician for evaluation.

Infection: Itinfectionit possible you have bacterial vaginosis caused by a bacteria. It could also be old menstrual blood. If it has a fishy odor, most likely it will be vaginosis. You also have to worry about chlamydia if you are having pelvic pain. I recommend to have a vaginal exam with a wet mount test to investigate the possible cause.