If there was no diastema before, the condition is commonly associated with periodontal disease, which results in so-called pathologic migration. Seeing a periodontist is advised.
i dont know if you are missing any teeth but even without missing teeth shifting can be normal. its always a good idea to contact a dentist when you notice any changes in your mouth but if you have regular dental visits you could wait until your next scheduled appt. if you do not go regularly schedule an appointment and get it checked. its probably nothing but if it concerns you enough to post it should be checked by a professional. good luck and let us know how things go.