It's almost been 12 months since i stopped taking the depo shot and still haven't had a single period. my gp was administering it monthly?

Not unusual: Women do report that it may take as long as a year for menses to return after being on Depo, and if you were getting monthly shots instead of 3 mo, then there may be residual hormone in your system. Other things can affect return of menses, including thyroid disorder, severe underweight, PCOS, etc., so I recommend getting an evaluation, especially if you are trying to conceive.