When you buy a quartz or any kind of crystal for you, the first thing that you need to do is clean it from all the energies that were before you within the stone. This is something really easy to do.
All you need to have is water and salt.
First, you need to put the crystal under running water; after that, put some water in a bowl and add some salt (if you are near the ocean and can have sea water it would be good instead) and put the stone in the salted water. Leave it outside your home under the moon light and the next day take it and wash it again with water; then go outside and leave the stone under direct sun light for a while in order to energyze it.
After these simple steps your crystal is clear and will have your own energy; very important: do not allow anyone to touch it. You can clean your stones once in a while, when you feel it's necessary or if anyone accidentally touch it.
When you feel that your crystal is not vibrating with you, it's because the mission of that energy working by your side has just finished, so what you can do is bury the crystal.
Love & Light.