How long can a brown recluse spider bite stay on your body?

I have a spider bite at the moment and it's so painful! I got it on Monday i think. When I looked online, it said it will last a day or 2 if it wasn't venomous, but if it was venomous it can last over 1 week. If it is still there after 2 weeks and it is not getting better, go to the doctors/hospital.