Hypertension?

I'm 18, in my last year of school. When I was 17 I went to donate blood at my school (the organisation comes to our school every few months). I've never donated blood before so I decided to try it out. They weighed me, tested my iron, everything was fine. Then they took my blood pressure and I had 190 over 101. The nurses were in a frenzy and called an ambulance. I also had to go for regular checkups at the doctor and was basically watched and monitored every chance every medical professional got. I'm always stressed about school, but I never thought it would get THIS bad. My mother has high blood pressure, but it's due to the fact that she eats a lot of salt (she's the kind of person that eats salt from the shaker) so it's not heditary. I doubt stress on its own could bring my BP up this high so I can only assume there's some underlining medical issue. I'm also prone to stomach ulcers and kidney problems (but not kidney failure per say) but it comes and goes. Today my health is fine, but in a matter of days with no apperant reason my BP shoots up and I'm under watch again. What's going on?