Blood pressure changes

I am a nonsmoking 26-year-old female and have always had good blood pressure in the past. About a year ago I participated in a 6-month exercise study (basically I just had to do light exercise for 30 minutes every day) where they took my BP monthly and it was usually around 115/75. Now, about 6 months after I finished that study, I've had to visit the doctor three times for other things (heart palpitations that turned out to be harmless and some digestive issues), and each time my blood pressure is always in the prehypertension range...about 130/85. Last time it was 135/88.  

So I'm wondering, why would my blood pressure jump up to that range in a fairly short amount of time? It's true I'm exercising less than when I was in the exercise study, but prior to that I was fairly sedentary and had lower BP. I have also lost 15 pounds (so I'm no longer overweight for my height) and started eating better since my lower readings were taken. It could be because of my birth control, but I've been on it for 6 years. Neither of my parents have high BP problems, so it's not hereditary. Could ongoing digestive issues be the cause? I am worried that if it gets much worse I'll have to take BP medication, which I don't want to do.

[Inkling]

Oh, and a couple more things I wanted to add to my post -- I have recently quit caffeine and started taking Prevacid since I seem to have acid reflux or something (will be having an upper GI test in 3 days).