Prescription medications are fine, but they need to be in the original container with your name on it. What pain medsspecifically, because some are controlled narcotics and will face much higher scrutiny, especially if you are bringing multiple months worth.
As for morning after pills, only Quebec requires a prescription, so no issues.
In a province or territory where plan B® is kept over the counter, you will find it in one of the following sections: Birth Control, Contraceptives, Feminine Hygiene or Family Planning.
In provinces where plan B® is kept behind the pharmacy counter (Quebec and Saskatchewan), the pharmacist may ask you a few simple questions before giving you, or prescribing you (in Quebec).