If there is a burning sensation on the left side like in the middle but the pain only occurs every now and then. Should I be worried?

Needs work-up. Suggest you see your family doctor. You certainly need a urinalysis and probably either an abdominal ultrasound or an abdominal ct scan to discover cause.
Vague complaints ok. It's hard to figure out what part of the body you are talking about. If pain is once in a while and is not bothering you it may not be of consequence. Relax and see if it returns.