Question about water pressure and swiming?

Yup, Archimedes Principal: An object is pushed or bouyed upwards by a force equal to the weight of the water it displaces.

If you weigh less than the ammount of water you displace you will float. If you weigh more than the water you displace you will sink.

"Why is it that when i swim at the surface, i have to keep myself from underwater"

Gravity vs. the part of your body that still out of the water.

"but when i actualy dive (without equipment, that is) I'm getting pulled to the surface?"

The air in your lungs when you're holding your breath.

When you are swimming your should be planning your body as part of your stroke. This enables you to raise high enough to use your arms out of the water. You will find if you stop swimming most people will float but not in a position that would allow them to swim.

The force that "lifts" you to the surface is the same force that allows most humans to float. buoyancy.

Look up buoyancy and it will explain the concept to you.

Remember Archimedes´ principle !

I would like to know the answer to that also

this is natural.