All honey will crystallize- it's normal. Depending on the honey moisture content %, and the actual type of flower nectar it was made from, it will happen sooner or happen later.

You should not heat honey jars in simmering water or in a double boiler- that high a heat will destroy some of the wonderful micro nutrients and enzymes you want to retain.
Instead, simply put the closed jar of honey in a pot or bowl of very warm water from the tap and change the water a few times until the honey has become liquid again. Another way is to place the honey in your closed oven (oven NOT turned on of course) with the light bulb on for a day or so- if your oven has a light that can be left on with the door closed (my oven does, it has a window in the oven door and a separate light switch).
Honey will slowly re-liquify at about 90-110 degrees F. Never microwave honey to liquify it.
Just leave the closed jar in a bowl or pot of hot tap water and change the water a few times to keep it warm.
Once you've re-liquified the honey it should stay that way for a while. Hopefully you'll eat it soon anyway, since it's good for you!

No need to ever store honey in the fridge- real pure honey does not spoil. Besides, cold honey gets too thick to pour. Honey has been found intact and edible in the Egyptian tombs, several thousand years old!
I keep honeybees.