At your age this is not common, but try to find out the cause and remove it from your life. Try to forget the things which makes you  trouble and try to support some supportive company. Do yoga and meditation try some physical workout.

It can be stressed induced or a unstable mood. Please visit a psychologist and address the same

Since you mentioned three months, it's good to reflect if these changes were brought about anything in particular. Could be changes in lifestyle, work life, physical health, life events etc. Also assess any change in your sleeping environment etc. It's hard to give an answer without deeper assessment. Medications are usually the last resort and counselling can be beneficial in making little changes that go a long way.