Since PES 3 i was trying different software and way to capture/ record the gameplay in best way possible. For sometimes i found that Fraps was the best chose for me, but its capture without any compression and video files was huge.
Today OBS is great for that but you need to found right settings for your machine. If you have problem with capturing that mean you setup wrong settings or your PC is really weak .
You say that you using screen capture source ? Open the game, run OBS, add source "game capture ", mode : capture specific window, on window pick the game window. Now the OBS will capture the game window only, nothing else.
From here you need to found the best output/recording setting and most important, encoder for you. I can try to explain you every single options and setting from bitrate, rate control, profile and tune but that will because really long post and.. I'm kinda lazy now, but there are tons of tutorials and info outside.