I have this thing on my arm for about 1 week already. I don't know what it is exactly. From what I found online, I think it is spider bite, the bite shown on this article (https://thetab.com/2014/09/26/a-venomous-spider-bit-me-in-halls-and-now-im-scared-to-sleep-21598) looks very similar to the one on my arm. Additionally, I got a spider on the curtain of my room, so I assume it bit me while I was sleeping.

Anyone has experienced something like this? What should I do?