Irritation when shaving.......?

I'm a swimmer so I shave some parts of my body, but I have a hard time shaving the line from my naval to pubic area. When I shave this part it always gets irritated and black dots which I'm guessing is hair appear not that long after I shave. I use shaving cream and use water too but it always gets irritated. What can I do to prevent it because it's embarrassing. I have also used electric shavers