Solution: Slow down to give yourself time to develop better rotation.
If you feel like you fight the water when you swim you probably have a short, slightly scrappy stroke with poor rotation. To develop your body roll you need to give yourself more time on each stroke to lengthen out. To do this, consciously try and swim slower and rotate from the hip as you reach forwards on every stroke. Imagine you have all day to get to the other end of the pool.
Since you have slowed down your stroke rate (strokes per minute) you probably won't go any quicker at first even as you lengthen your stroke. When you have developed a longer stroke technique you can speed things up again and break into new speed territory.