how to make keyframes not affect the ones before it...

Im animating a camera to move. The camera is at point a. I add a loc rot scale keyframe. I then move the timeline ahead and move the camera to point b and add another keyframe.
the animation of the camera moves how I wanted it to.
I then move ahead in the time line, move the camera to point c and add another keyframe, but now when I play the animation the movement from point a to point b has changed. I know it has something to do with curves but I dont want to have to go into the curve editor and straighten them out everytime.
So my question is…
How can I make a kefram not affect the keyframes before it?

in the dopesheet, select the keyframes, and press V. then select “auto clamped” that will make sure at frame A camera is at position A, and at frame B the camera is at location B, etc