What Causes Fatigue And Excessive Sleepiness While Suffering From High BP?

I am tired continuously, fall asleep in my chair, have no strength, no energy, and can do almost nothing. 6 weeks ago I had a battery of tests in the hospital because of high blood pressure and shortness of breath. My heart tests all came back fine, no blockages, valves all working fine, everything working fine. I still have the shortness of breath and was sent for a pulmonary function test, which showed mild airway obstruction signs of asthma consistent with asthma; the doctor changed my medications which seemed to be helping. Last week I had a pneumonia shot. After coming home from the hospital I started a walking program consisting of 5 minute walks three times per day. Two weeks ago I increased that to six minutes three times per day. This was going fine, but for the last week to 10 day, I am so tired all the time, have no energy, fall asleep several times during the day, have vague body aches. I am forcing myself to continue walking each day, but it is forcing myself to do so. Can you give me any suggestions as to what may be causing this much fatigue, sleepiness and lack of energy and/or interest in doing anything but sit and sleep. Also, if you can t give a diagnosis, could you suggest what type of doctor I should try next? Thank you.