I'm not afraid of water or cold, but very sensitive to cold water, especially on my belly, waist and back. When other people claim the water's warm, I have difficulties to breathe. Can I do anything?
I have a problem with 'not so warm' water myself, although it isn't as extreme as yours.
What I do:
Take a cold shower right before going into the water. This will get your body used to the temperature and make the water you are going to swim in appear warmer.
Take cold showers while showering. I do this from time to time to get myself used to colder water. Start showering warm and reduce the temperature. Turn the temperature up again and repeat. Whether you reduce the temperature gradually or by abrupt comes down to what works for you.