10 games isn't much to be meaningful.
But this is a common complaint. It could have a lot of reasons. Maybe you are playing at times when you aren't able to focus. Maybe you are distracted by real-life problems. Maybe you are trying to incorporate new ideas into your game and are getting them jumbled/misapplying them.

Hello guys. I started to play chess more actively like 5 months ago, and so far studied it very hard. I thought I made big leap in progress because I can find "killer moves" in chess videos, I can play good games against higher rated opponents.... but it seems that the more I study, the worse i get. Last 10 games that I played here looks like I'm moving random moves: I often gives away pieces for completely free, I overlook checkmates in one etc. I think that I know a lot of theory about game in view of fact that I have been studying only for 5 months, but I can't beat opponents that I could say 2 months ago. It is very frustrating and discouraging for me. Why is this happening ?