One thing that has been drummed into me by friends in the medical profession is that you should never self-diagnose. That's what the doctors are for. Even more dangerous, you should never ever self medicate!
BP varies throughout the day, peaking at around 11am to 2pm from what I've gathered. It should be at its lowest when you first wake up, and just before you go to bed (assuming you're feeling sleepy and ready for bed, and not acting hyperactively of course

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If the doctor suspects white coat hypertension, they would probably request for you to wear a portable monitor which records your BP throughout the day which can then be analysed by the doctor on your next visit. I've not had this done, so I can't tell you in detail what you need to do with this device - your doctor is the best person to advise you on this...