What Causes Chronic Fatigue, Light Headedness And Palpitations?

Why do I feel light headed all the time, very weak and fatigue but Im just lightly anemic. Also my heart rate increases tremendously when my stomach having hard time digesting. Follow that my whole body shivers but I m not cold. I have done multiple tests include engiogram and nuclear test for my heart. Colonoscopy and endoscopy. CT for my abdomen area. Everything came back normal. I do have acid reflex/heart burn, and digestion difficulty. I m taking ranitidine and digestive enzyme. Also I ve been on poly-irons and B-12 over a year now but doesn t seem to help my mild anemia. Other drugs I m taking also are vit-D2 and simvastatin. Are there side effects for being on any of these drugs for too long?