Hardstuck Gold need tips.

Hello guys im stuck in gold for 3 Seasons(Season 7 is the 4th time). For all these seasons i've been getting promoted to Gold 1 and then demoted to Gold 5 and im start getting mad. I have tried the one trick ponny thing and it worked for a while but still doesn't work. I also tried to main like 3-5 champions and still worked for a while and then nothing.

I main mid and jungle right now. (I used to main mid/top or mid/bot but right now i find it extremely difficult to win in bot and top) I can win my lane for fun but still lose the game hahaha.

Recently i figured out that im doing something wrong during the mid-game and then i lose the game but i can't really understand what i do wrong. 90% Of the time i play full defensive and try to find the perfect opening to go in. Also i would like to mention that during a teamfight if i consider that we'll lose it i don't even join the fight(That's probably a good reason why i lose).

That's all i had to say and i would really appreciate it if you can give me some tips :)

Note: I am not a maniac who's just trying to get in high elo, im playing since season 1 and during these years i lost my interest in getting at high elo, i just want to find out what im doing wrong and improve.