How long for blood pressure medicine to work?

I am 48 years old 6' and 245lbs. About three years ago I had my first bout with pre-hypertension. I had a sudden blackout and passed out for about 20 sec. It seems afterwards I was always feeling light-headed and dizzy. After a doctors visit I was told my blood pressure was up , but could be managed with a diet change, exercise, but no pills required. Now, I did have some attributing vices that had to be curtailed. I smoked about a pack a week and on average drank about 10 drinks per week, mostly beer. To offset this problem I stopped using caffeinated products, lowered the fat in my diet, and exercised off and on about three days a week. I was feeling better and looking better. However, about two weeks ago I had heart palpitations so bad that I had to go to the emergency room. After test they could not find anything conclusive, but recommended reduced stress and more rest. Then about two days later my blood pressure just shot up and the highest reading was 210/120. I went to my doctor and they ran a battery of test. I went to cardiovascular doctor, had a stress test, EKG, and a look at my heart valves. All came back fine. Then they did a head scan and it came back fine. They put me on 5mg of Amlodipine Besylate last Tuesday. Since then I have not exerted myself and took off from work. However, my blood pressure readings are still high and fluctuate between 149/95 to 180/100. Today I tried some light walking and I felt my pressure shoot up again. My question is how long does it take for the medicine to start working and is it normal for me to go from running a mile and lifting weights one week to not being able to do a light 1-mile walk a week later?