As much as I love khaxiz, he is my main in the jungle. He is not a carry champion if you don't play him right. The only way is if get 4-5 kills first 10 minutes of the game, to the point you just 1 shot everyone you come against to force a surrender. Late game, yes he has dmg, but the minute he is CC locked, he is dead.
Also too you need to know when to go in on the enemy back line. You can't just go in whenever you feel like, you need to wait until champs cc was used, or someone got separated. Thats the rule of assassins, wait for someone to stray and pounce. Thats what I always do now since I had the same issues you did, then I evaluated my game play, and found that I would die way too much during team fights. If you deserve to be in silver/gold wherever, you will get there in time, just takes time and patience.