Don't be surprised that your BP is always changing due to posture, time of day, if and when a Doc is present, when the temperature is different, etc. That is the whole point of your BP. It's designed to adjust as needed depending on your mood, surroundings, stress levels, have you just eaten, etc. Even differences in right and left limb are normal.
If your BP often seems elevated, and you have some concern about whether you might be hypertensive, you should ask your physician about doing an Ambulatory Blood Pressure Monitoring (ABPM) study. This is designed to capture your BP throughout the day, and night, so that you have a true picture of your BP and how your body is reacting to all the factors mentioned above.