obs lag

I was interested in start streaming and then I realized that when i had the OBS opened that my fortnite was lagging, i thought that was my settings in OBS then i stop streaming, i checked fortnite and i was lagging then i closed OBS and it was running just fine! CPU: i7-7700 CPU @ 3.60GHz GPU...

Since i use obs i have problems with the preview and stream or record that it was laggy. I don't know what's happening but i need fix it. The problem came especially with fast movements on the game. This maybe affect on the encoder i don't know. I use x264 (veryfast, 720p60, 6000 bit-rate)...