Okay, well, I don't have a good track record with spider bites. I get an allergic reaction where whichever part of me is bitten (usually the leg) becomes very swollen and then I can't walk. It becomes very red and itchy and high risk for cellulitis.
The sharp burning sensation and itching means "allergic reaction." Taking Benedryl is a good idea, to help reduce swelling. I would call your doctor and go to urgent care if it's after office hours for your PCP. I would also take a ball point pen and draw a circle around the bite so that you can tell if the bulls eye gets much bigger. Each time it does, draw a bigger circle around it, okay?
Please keep a close eye on it. If it shows any signs of infection I would go directly to the emergency room. Oozing, pus, hot red skin, tenderness, fever... please keep a close eye. If the pain becomes worse or the reaction gets worse instead of better, especially the swelling and you find it's more difficult to walk and/or put shoes on and/or take on and off your pants, go to the ER. If you feel dizziness, light-headedness, take note of that too. Keep a journal of anything unusual. Take photos of the bite now so that you can keep track of any changes better.