Maybe the problem is that you did many without thinking, which helped you to climb, but not improve. You have to always think, when you are playing jungle, since you have the most pressure on the enemy team. CSing for example. I thought I was a decent jungler, I had good farm (7-8 per minute), but once my high diamond friend checked my games, he said that I absolutely suck at it.
When you are not farming efficiently, you lose a lot of farm because of jungle gaps. That's why you should always track your jungle camps' timers. You can download blitz or some other map to do it for you. Here are some tips that my friend told me:
- You should always finish your clear, no gaps between jungle camps. When you start farming bot jungle, you should finish it in the top lane.
- If you see that your jungle clear is messed up, you could wait for your camps to respawn, while doing something else (ganking or counter-jungling). It is also a good time to reverse your clear (start clearing from another side).
- Think before clearing. Check the timers and lanes' states, so you could choose, where to start and head to after farming.
- Don't hesitate to push lanes in mad-late game. If no one is coming to get the farm and minions are getting close to your tower - push the lane, you create pressure on the map and let your team get more favorable fights.
Also, you trying to carry all the time might be an issue too. Let yourself get carried sometimes. Especially in high plat, where players are more decent.