Why is my door ajar light coming on when I am driving?

What is your question?

It started coming on just turning corners, when my leg would put pressure on the door. Now, it constantly turns on and off, making the locks go crazy and the interior lights come on. If i push on the door from the outside, the lights go off. Is this a latch problem, electrical problem, or should I just replace the door? How much will this cost (aka is it worth it?)