Go to the doctor, Shima.
I had a spider bite and it looked similar, at first. Actually, it was several in the same place. Apparently it had gotten caught in my covers while I was sleeping (just one more reason to give up sleeping
) Within a few days it looked like a huge bruise, but it didn't heal for months. I went to the doctor on the fourth day, as it was still growing, and he was able to counteract some of the poisons. It was not painful right at the punctures, because it was a type of nerve poison, but the surrounding area was very painful from quick swelling. Kind of like a supernova zit, only the bite was causing irreversable damage to the tissues.
Usually a tick bite will have a single puncture, and quite often a head, broken off inside. No problem to the tick population for one to loose its head, since even as it dies it can find a safe spot and if it's a fertilized female its body will still protect the developing eggs. So, you'll have many more on the way.
Go to the doctor, Shima.
I like your back, too. I get these ideas ...