I've had one day periods every month for about 4 months now. Definitely not pregnant although I was on the pill previously for my skin. Please help?

Talk to doc. I would have a face to face talk with your doctor to discuss this issue because the underlying cause could be a number of things and it would be difficult to go through those things over this outlet, especially without running labs and doing an exam. He or she may be able to precipitate more normal periods for you but the cause should be investigated. Best wishes to you!
Irregular menses. Given that this irregularity has persisted for an extended period, I would follow up with your Gynecologist for further evaluation.