My Retina Macbook Pro can not switch to the advanced graphic card on both Max OS and Win7.

Setup: my rmbp is currently connected to a external monitor, and the external moniter is my main screen.

Issue: I've been gaming on both Mac OS and on Bootcamp, the fps looks pretty good. (about 60fps on league of legends and my rmbp is connected to the charger all the time when I'm gaming) . But today, when I brought my rmbp with me from my class back to dorm, I found out my rmbp failed to switch to the advanced graphic card even when it was charging (same game - league of lengend, only 20 fps, I am very sure there is no change in the game setting, I also tried other games, the performance is also bad). So I tried disable the auto-switch in preferences; restart my rmbp; restart my rmbp without external monitor; and I also tried it on bootcamp, still, can not fix this problem😢😟. I wish I can get some helps. Thank you.