Heavy lag

Since the first time I played this game, I have always been encountering lag. I have done everything I can in order to make it better, but nothing has helped, though a VPN helped slightly.
Now, here's the thing. I'm currently at my girlfriend, playing on her PS3 with her on PC. I had extreme lag, worst case scenario lag. She had no issues whatsoever.
She has never had lag problems, and even when playing at my place, with the same ISP, identical cables connected to the same switch. It doesn't matter which system, she either has no lag, or minimal, while I can barely play.

We have switched cables around. We have done just about everything you can do. The same scenario occurs, and I ALWAYS have problems while she can play as the game was intended to be played.

What can I do to fix it? The support isn't able to help. They redirect me to the same FAQ over and over again, even though that information hasn't helped a single time. It's so bad that I'm considering not playing ever again.