What Is The Cause Of Sudden Increase In Blood Pressure?

I am a 44 year old woman in very good health. I live an active lifestyle and walk between 3-6 miles 4 times/week, I bicycle and hike, I drink approximately 1 gallon of water a day and I have an extremely low-fat diet. I am 5 feet 8 inches tall and I weigh 255 lbs. Two years ago I began gaining weight for no apparent reason, going from 157 to 255 in a matter of 18 months. I also began experiencing edema in my extremities and face. I went to the doctor several times over a course of 3 months and underwent every imaginable diagnostic procedure you can name. . . .all of which turned up nothing out of the ordinary, which was surprising, to say the least. Though my cholesterol and blood pressure have always been normal, I am alarmed by a recent spike in my blood pressure. I took the pressure at a pharmacy 4 days ago and it was 157/123. The following day it was 148/120, and today it is 144/123. I experienced eclampsia during each of 5 pregnancies, severely enough to be induced at 31 weeks with 31 weeks with 2 of my children, and at 34 weeks with another, so I understand the inherent risk of having high blood pressure. The thing troubling me now is that there is no APPARENT reason for the spike, or the weight, or the edema. I would really like to know what can be done to mitigate these symptoms before I develop a very serious health condition.