How can i beat a fast kickboxer?

most of the kick boxers at the club i go to have only ever done kickboxing, iv been going 3 years now and only just started sparring, before kickboxing i did normal boxing which is very different, im used to moving slow and getting in close to my opponent, i find it impossible to do so with kickboxing, i know how to block the kicks and know how to throw the kicks but they always keep me at a distance, when i finally do get in to them they always get me first and move away, iv been doing shadow boxing and a lot of work to try and improve my speed but i just cannot get my opponent. Im not a light footed fighter, never have been, never will be but it just really annoys me how i cannot get one hit in. I get a hit in every so often to be honest but most of them skim my opponent, very rarely i get a good hit, how can i improve?