1: Not ramping sets, thinking 5x10 meant 5 sets of the same weight for 10 reps, and that you only increased weight when you could get all sets fpr 10. wlcome to Stagnation, population, me. Thanks to professor X for clearing up that. Strangely, this is how alot of (small) people here train.
2: uncontrolled bulking, from 2000 to 6000 kcal from one day to the next. Welcome to Fatass, population, me.
3: Spending my teens hovering around 80 kg, not wanting to 'get fat'.