I have been on several high BP medicines for many many years. Over these years, I have slowly gained weight and cannot lose it. Of course, this weight does not help lower blood pressure, so I get more meds! It is frustrating!
Most people gain weight as they age. There has to be a change in eating habits to offset this, or there will be a gain. It will be slow, but sure!! And it's hard to get rid of!
Another thing is that some, but not all, people with high BP retain fluid. Are you on any kind of diurectic?
In other words, you gain weight from retaining fluid or too much food as you get older. You need to drink a certain amount of fluid so that leaves you with the unpleasant task of cutting back more on your calories.