Right, well the first thing you need to do is take a pregnancy test because your symptoms could be caused by something else, such as the depo. It can take ages for your body to get back to normal after stopping the depo.
Are you planning a baby? In other words, have you been having lots of unprotected sex or just a one off mistake? If a one off then it would be easier to guess how far along you might be and whether a test would be effective yet.
Good luck!