Winning 90% of games and then losing 90% of games - A Very Frustrating Pattern

Hello, I'm looking for some advice and other people's experiences.

I'm a Gold V support main who plays mostly normals. I seem to go through patterns of doing really well and then playing abysmally. It could be a month on, a month off. During a good month I feel like I'm improving and learning and feel great about getting better at League... and then it seems that all goes out the window in a few weeks. I feel annoyed and hopeless, and find it really difficult to see what I'm doing wrong.

I'm in one of those times now and have lost 18/20 past games. I feel confused and frustrated and would love some input from people who know what I might be going through.

Thank you so much.