Feeling slight pain in left side waist area (since 2 days) when i get up from a sitting position. goes away on its own. should i be concerned?

No: no unless it is associated with other symptoms like fever ,chills ,anorexia, and vomiting .if pain persisted or becomes worst see a doctor.

Left Sided Pain: If you have no other symptoms like fever nausea or bloating you are probably ok. But when is the last time you had a bowel movement? Constipation can cause left sided pain. Also are in the ovulatory part of your cycle you may also experience pain when a follicular is about to burst. If you have no other symptoms consider taking Acetominophen or Ibuprofen to see if the pain is alleviated.