I Had What I Assume Was A Spider Bite (I

I had what I assume was a spider bite (I did not actually see the culprit) about 2 years ago. It got really itchy, and within minutes it became a raised welt with the surrounding skin being pink. By the next day it had blisters at the center of the raised, pink welt. Eventually the blisters broke, and slowly it healed, and soon there was no sign of it at all. Several months later. I felt that familiar itch in the same exact spot, and as I scratched, it became a full blown raised pink welt with blisters. I thought maybe the toxin from the original bite might have lingered and it caused this welt to return. Then that welt went away as if it never happened. And here I am probably more than 2 years after the original bite, and it just came back again. What can it possibly be? It is driving me crazy.