What Causes Bleeding Between Periods?

Hi there, I do have a question which is worried me as since early this year is seem like my menstrual is not normal as came twice a month ? My dates came on 02/02 to 11/02 and it came on 28/02 to 11/03 and last was 25/03 to 06/04 and now it seem like today 18/04 again.. Am I normal ?