Well your recent statistics say you're not doing that much wrong, and especially when you're playing Support Nautilus, don't undervalue assists cuz you do seem to get plenty of that.
Guessing from how you listed off 3 things and then said "other stuff", I strongly suspect you're trying too hard to learn too many things all at once and are failing at that. Focus on one thing at a time if and when you can and get good at that one specific thing before learning the next concept. Again, I must emphasize that your statistics overall are saying some pretty alright things for you, so at this point I think what you really need is focus. Maybe focusing entirely on Support since that seems to be your best role at that moment, and it's the least mechanically intensive (short of you throwing your Q every time its off cooldown) so you can focus on your macro skills.
And don't beat yourself up too much. Celebrate victories and analyze losses (with a cool head), that's how you get better.