Reversing...Don't think my caravan likes it!

Bought my first caravan a month ago and just returned from 3rd trip. When I reverse on to my drive, my clutch pongs, even though its a tiny slope.( It did the same thing when i reversed it on flat surface on site.)I've also noticed that the rubber concertina-like thingy on the hitch is all squashed in to the extent that my Alko hitch lock won't fit and no amount of pulling will extend it.

A friend suggests that there's a fault with my caravan braking system, so when I reverse the brake comes on, making it hard for my car to push it back and causing the concertina affect. Any ideas?