High blood pressure a tnight

I was diagnosed with high blood pressure in the fall of 2009 180/120. I'm 24 fairly healthy and it doesn't run in my family. I've been to the doctors, my blood work is fine. Had ultrasounds on kidneys and an ECHO, stress test wore a 24hr monitor and the whole !**@! was a bit high, changed diet everything is where it should be now. I was put on 5mg Norvasc, it dropped to approx 140/85, I haven't been checking it regularly enough but over the past 2 weeks I've felt an increase, I was 143/90 at the Dr. so they increase my dose to 10mg Norvasc. I still feel high at night, but don't want to go to the hospital to get it checked because they won't let me leave if its high. What else could cause this high blood pressure? I have quite low stress never smoked have 1 coffee a day in the morning. I'm at a loss and am getting very discouraged and disheartened.