pain during intercourse

i like sex. my wife desire is low and when she has sex it is painful and she would rather have nothing inserted. main position is like missionary but her legs closed and straight while my legs are straight but outside hers so penetration is less and not as deep. she says part of non-desire comes from japan where they mainly eat vegetables, japan diet where desire is not as much as in america. what can increase her desire and heal pain (whether physical or emotional or both).