Lisinopril and aortic valve replacement

I was prescribed lisinopril after I underwent open heart surgery for aortic valve replacement last July. Initially I was on 40mg, and was successively reduced to 5mg, which is where I am now. Basically, my dosage would be lowered after I would start to complain about side effects (dizziness, fatigue...), which my cardiologist would attribute to my recovery -- i.e. my blood pressure would stabilize, hence the higher dosage would lower it too much). Well, now I'm down to 5mg, and I feel worse than ever. I'm dizzy all the time, I have severe aches in my joints -- particularly in my knees and elbows, stiffness in my hands, pain in my feet, extreme fatigue, weakness in my arms, shortness of breath, and mild chest pains. My cardiologist maintains that it's not the lisinopril, yet after running full bloods, my primary doctor can't find a single thing wrong with me. I tried getting off the lisinopril for a little over a week, but I didn't feel any better. So, my question is this: does anyone else feel as crappy as I do, and how long does it take to get this drug out of your system? I'm only 34 yrs old, I'm not overweight or otherwise out of shape, and this is really affecting my ability to work and to spend quality time with my wife and 10 month old son. Ugh.