Weezer

Hi I play guitar for two years now. My biggest difficulty are barre chords. I can play them flawlessly, but after 1 or 2 minutes of a song that consists of barre chords my right hand ( I am a lefty) starts aching and my playing gets inaccurate. I think the pressure of my finger on the fretboard is too high, but if I try to play more relaxed Rocksmith refuses to recognize the chord.Anyone else with the same problem or any hint for resolving this? Thx