Hi, There are many kinds of hydrangeas, some flower very easily while others are not only hard to get to bloom but also hard to grow. Hydrangeas need well drained (which a sandy soil is all ready) and very fertile soil, (sand is not very fertile). Add more organic matter to your planting site. Since the hydrangea is all ready planted you will need to add compost to the root area and work gently into the soil. It would be worth the extra effort of digging the plant up and amending the whole area or you might not be able to get enough compost down to the lower areas.
Oakleaf, PeeGee and for some zones a Nikko Blue are not too fussy. Do you know what kind of Hydrangea you have? For more specific information I need to know what kind it is. I suspect you have a type grown in a greenhouse as an Easter plant. I have one of these in a perennial bed that is many years old and has never bloomed. It has lush green growth but no blooms so I think of it as a green background bush and if I ever had a bloom it would be a tremendous treat. I also have Oakleaves and a PeeGee that only need attention in a draught, otherwise they bloom freely and make wonderful dried flowers.
Tell me more about your hydrangea.
Bye for now, Diane