I have a problem with runes

Hey there. I got a problem, a big problem. I turned level 27 recently and i saw my winning streak turn into a losing streak. First, know that for me, a victory is having a positive kda, but right now, i'm feeding to every game. Every game, either victory or defeat, people swear against me at each death. Plus, each time i play i'm angry to myself, for not being good, for feeding, for not understanding what's happening to me. I'm now scared of playing, in fear of having a negative kda, and having a negative humor for the rest of the day. But i figured out that i am not the one who is bad, that if i am feeding, it's not because i'm a noob. The champs were just always doing more damage and had more hp, mr and armor. I figured what it was:

Runes

I'm lvl 27 and i don't got any runes. You'll tell me, ''just buy runes then''. But i got another problem, i got battlebunny Riven in an hextech box. Since then, i'm collecting IP to buy her and get the skin. Right now, i'm close to 4800, i really really wanted to have her since i started collecting IP. But, i know i could use the money i have right now for runes, but i would be extremely sad of losing the opportunity to have her. So i was thinking about buying Riven first, and buying runes ASAP after, i was thinking about buying runes for Riven. But, maybe after i got her, i won't be able to win any games to get the IP for them, due to the emptyness of my rune page.

I am asking for your help and suggestions about the situation i'm currently in. I don't want to do any bad move.