I have a white thick discharge. sometimes white and clumpy. and it itches and burns when i have sex. is it a sign of and std?

Vaginitis: This sounds like a vaginal infection rather than a uti. These two conditions however often run together and it may be best for your doctor to check you for both conditions and treat accordingly.

Vaginal Discharge: It surely doe not sound like any common std. Given the itching and burning i think you should be seen by your family doctor today.