Now I see that solving your problem will take more than just following [http://www.stadion.com/phpBB3/viewtopic.php?f=22&t=380#p1264]jrlefty's advice[/url] on improving your condition and correcting the form of movement. This is because you have neglected all fundamental skills.
The form of your roundhouse kick shows that you have not learned the skills that are prerequisites for learning the roundhouse kick (see my column number 7
). From the way you carry your arms I can see that you have not learned punching well, let alone the simpler kicks, learning of which ought to precede learning the roundhouse kick. There is a purpose to teaching kicks in a certain sequence on the video “Power High Kicks with No Warm-Up!”
and that purpose is to end up with powerful and useful kicks and not liabilities.
Were you in good fighting shape, you could overcome some of your kicks' problems, but without the right form you'd still kick at half power or less and set yourself up for easy counters.
If you learned your way of kicking on your own, then you can still fix it by starting anew. If this is how someone else teaches you, then change the teacher. Find someone competent.