Dnd cleric Goliath

Hi,
This is the first time I play DND and, with the DM, I choose to play a Goliath.
I was thinking about the background story...
As I'm a cleric I have to have a holy item that help me to connect with Gods and as background I choose to be an outlander.
I came out with the following story.

Beginning
I was born in a Goliath's clan above the mountains and I spent there the first 8 years of my life.

Our village was on a Rocky mountain that was blessed by the god Thor with that with his thunders and storm gave us a lot of water and the precious stones "Shungite" to trade. If you don't know, Shungite' stones can give protection and has healing property.
Ours Shungite's cave were the biggest of the country and the most pure of the world.

One night an army came and could kill all the adult people of the clan and they took all the kids with them to enslave us.
Since that day I haven't returned to my native place.
They were bringing us down to the mountain when the night was to cloudy and dark to keep walking and the guards decided to take a break for the night.
I knew that it was Thor, I knew that he would try to save us and exactly when they let us sat down a thunder started from the darker cloud and hitted the Shungite of my necklace.
That thunder disseminated all around me and paralized everybody around. I tried to save the others kids but I couldn't cause they were already bounded to the trees.
So I decided to run away as fast as I could and never get back unless one day I'll be strong enough to revenge my clan.

Running inside the forest I couldn't see a lot. I risked a few time to fall down from the ravine and I desired to see a little more I asked Thor to help me with some light. He heard me and in that moment the stone in my chest light it up and I could see in front of me.
I didn't realize that night but since then the stone fused with the skin in my chest.
That's why everybody know me as "Stoneskin"

Since that day of 7 years ago I lived in forests and I do some works as mercenary and that's why right now I'm in never winter.