Check your timeline and make sure you have not put an extra key point at the begining (I did this many times when I started) just right click on the timeline and zoom out to make sure, if you have an extra one there just delete it. Or open the options for your camera on the right you will see the function box (the little box with the half white thing in it) right click on it from there you can edit the function. Or use the syncro plugin as DMM said (This is what I prefere I use cinema) to get the best for camera motion.