Dont give up, keep practicing, ask your guides for help about it.
At first give it a try when you are really relaxed, late at night, during the night( if you wake up) or in the morning... then just do it, trusting it works. Eventually it will, you will get the hang of it! It took me a while but now i do it well...
be aware though that you can never do it 'perfectly'. some times you will be off (switched), you will misinterpret the results, have interference, and all kind of stuff... having your hemispheres synchronized helps greatly, so meditation or (as cheesy as it sounds) Super Brain Yoga (youtube) helps for this, as do many other things.
Good luck hang in there!! dowsing is natural for all human beings, we do it all the time indeed! just most of the time we dont realize it.