First of all, make sure you've got your hand straight. Don't try to play barre chords with your hand and arm at an angle to the neck.
Second, make sure your thumb is at the center of the neck for bracing, not wrapped around or some such crazy thing.
Third, experiment to find a position that is comfortable for your index finger while still being able to properly barre the strings.
And finally, just practice. It will take some time to get used to the chord shapes and hand positions, but you'll get it.