Frequent backache and heels pain.

Hello, I am 34 yrs old female and I am over weight. But whenever I do litte workout (as little as dusting the house or a short walk) I get pain in my heels and back (lower back as well as upper). I want to do some exercise regularly to reduce weight as well as stay healthy but the pain scares me & I stop all workouts that I start. I work in IT so have very bad work schedule and whole day is spent in sitting. Please advice how I can improve it. Some background about both conditions: About 3 yrs ago, I consulted a doctor for heels pain and he told me its a condition called plantar fasciitis. I took medicine for 2-3 days only and then the pain started receding. Recently heels started paining again with very little workout/walk. For backache, 3-4 yrs ago i met with an accident where a car hit my taxi from behind. I felt huge pain for few minutes and cud not move but then the pain was gone completely. So I ignored and didn't get it checked. After that only i started getting backaches.