Don't worry, it's a mechanic called "new player protection" starts losing its effect at lvl 20. You will meet much stronger opponents at this point. So you didn't suddenly suck, it's just you're matched with better players.
For practice, I will recommend you to do 2 things,
1.One is improving farming. At your stage, get more than 140+ at 20min in bot games, and 120+ in pvp.
2.The other is controlling characters with ease and precision. To be specific, you can move your characters exactly wherever you want them to be, and cast spells wherever you want them to be.
For example, when you cast Q with morgana, you should only miss because you mispredict the enemy movement, not because you're not sure about the speed and range of Q, or not knowing where you are.
You need to know more about the spell range, auto attack range and animations, unit collision(don't get stuck in minions!)
Try to practice this, for example you play morg, you make a plan "I'm gonna walk out of brush, shoot my Q to X positon, and use W if it hits, and sneak back to the minions or brush right after that", then keep practicing it until you can do it exactly what you intended to do ( the right angle of Q, the right path to walk).
For other champions, this can be much harder, such as yasuo planning his harass with E.
After these two practices, you should be much better at the game, and can start working on some strategic side, which takes knowledge of the game, not practice.