There may be other problems here - repotting and watering, for example - but if the window is shaded, then that explains the leaf yellowing of older leaves and the pale new growth. Even sheers will block out most of the light that is usable by plants. So start by opening the shade throughout the daylight hours.
Not sure what you mean by "overflowing," but if the pot has drain holes, then I assume you mean the water flowed through those. That's okay as long as you allow the top inch of soil to dry before you water again.
