Thanks for your health concern.
Generally, the medication is not available without prescription.
You might be able to get one from a walk in clinic.
There is no reliable herbal / natural product.Progesterone
preparations like Meprate
etc are generally prescribed for this indication.
You can use it in two ways.
Take the drug twice a day for 5 days, and then stop it.
You would bleed within 3 - 5 days, maximum within a week.
Either use it to induce your period well in advance, or start the drug in time, and continue it for the duration for which you want to be without periods.
Once you stop , withdrawal bleeding results in a few days as described.
Obtain it by a prescription though.
All the best.