Though forgetfulness can be a normal phenomenon, excessive forgetfulness may result from various physical/psychological disorders. Thyroid disorders and Vitamin deficiencies, especially B12 and D are common reasons especially in young women. Also sometimes it maybe a symptom of depression, anxiety or stress. Dementia usually affects older population where memory problems are much severe. It would be advisable to get yourself evaluated if it is causing problems. Meanwhile, following a fixed daily routine, list making etc can help.