Having an unclear role at work place can be very confusing and demotivating. If left unchecked it can be a major source of stress in day to day life.
Next Steps
Generally your appointment comes with a job description. Try reading it again and see if that clarifies anything.
Try and have a word with your colleagues who are working at a similar position. Having a non accusatory but a clear worded conversation with your manager or HR might also help you to clarify.
However if nothing works then probably it has much to do with the work culture at your place.
Maybe then it's time to move on.
Health Tips
don't be in a hurry to quit. if the source of stress is not clear in your head then do consult a Psychiatrist