I am experiencing weight gain (time frame: gradual onset) . the following also describe me: high blood pressure (hypertension), obesity, and stret...

I am going to make: an educated guess. If the "stret..." of your question was going to turn into "stretch marks", then you are describing the condition Cushing's Syndrome--signs and symptoms due to excessive cortisol/cortisone. Have you been using steroids? Otherwise these symptoms are unusual in an 18 year old. Overactive adrenal glands/pituitary issues can also cause. See your Doctor/Endocrinologist ASAP for eval!