When I Go For A Walk, I Always Get Dizziness,

when I go for a walk, I always get dizziness, feeling faint, rapid heart beat and chest pain and my legs hurts .this only heaping when I walk I hope u can help me with the answer that my doctor cant find.I was 347 and now Im 307. I had a stress test but it didn't came out not normal .I'm taking high blood pressure medication