Is this poison ivy or a spider bite?

At the beginning of the week (Monday), I notice a small bump on my ankle when I took my socks off. Thinking it was another ant bite, I scratched it a few times, then went to sleep. The next day, the 'ant' bite had spread into a rash about one inch all the way around the initial spot. Stupid me, I scratched some more, washed it, and ignored it. The next day, the rash had turned into a series of blisters and even more rash . Now the initial spot was leaking a bright yellow pus all over the place, and very painful. I also noticed two swollen spots that I hadn't noticed before that looked like spider bites. I went to the doctor, and he said that it was a spider bite, and gave me oral antibiotics. The next day, my dad told me that it was poison ivy. I'm not sure what to think now, because I'm having similar symptoms to both of them. Two off the small blisters turned into huge, ready-to-pop blisters that hurts badly. One burst, but the other one has been there for days, and hasn't yet. In fact, it's getting even bigger by the day-no exaggeration here. What do you guys think it is? Also, the other smaller blisters are getting bigger now too, and I'm afraid that they will end up as big as the first two. Help!!