Period Every 12-13 days....

The past 2 months ive been getting my period every 12 days. The periods last about 8 days. I get all my normal symptoms acne, sore englarged breasts etc. There is no chance Im pregnant. I recently have been smoking marijuana 1-2 times a week but I don't think Its related. I used to have a regular period Im not sure whats wrong. Any tips or insight?