i am new to this gardening but i am sure sunflower always face towards the sun.

Yes, I believe they are said to follow the sun.

Perhaps you've had sunny mornings but it's gone dull after that! :-)

I have my first dwarfs this year, and they don't seem to be moving like the tall ones do, either. So maybe it is normal.

I have found that while they are in bud they WILL follow the sun, but once the flower opens out it remains facing east. Very annoying as I planted sunflowers by the wall at the east end of my garden expecting to be able to see their 'faces' from the balcony in the evenings, but I would have had to clamber out onto the meadow to see them! I now have them by the house so at least I can go into my own garden to see the flowers! :o)