Insect bite or something else?

I’m looking for some advice here.
I woke up this morning with this nagging itch on my right shin—almost like a mosquito bite, though there wasn't actually a puncture mark or anything visible at all. At the time, I had no idea how quickly this would escalate, so I just brushed it off and went about my business.
As the day progressed, things took a turn for the worse. The itching stopped, but in its place, a dark red lump—roughly the size of a toddler's palm—has emerged. It isn't massive in terms of volume, but it is incredibly hard to the touch and quite deep in color. There’s no pain per se, but the area feels noticeably hot. To make matters stranger, a pale white ring has formed around the base; the skin surrounding the lump is strikingly white, far paler than the rest of my leg. I honestly have no clue what I'm dealing with. It doesn't hurt, it doesn't itch, and it isn't even an issue under my jeans, except for a slight pulling sensation when I squat down. But visually? It looks absolutely terrifying—like something straight out of a sci-fi horror flick.
Help!
Of course, this kind of thing always happens right before the weekend—and naturally, my doctor only sees patients on Friday mornings, yet I waited until the afternoon to actually seek help!

Based on the description, it sounds like an inflammatory process rather than a direct infection—though it could be infectious, it doesn't have to be. It might just be a reaction to an insect bite... It is possible this could be erythema nodosum, which can signal an immune response triggered by things like sarcoidosis or tuberculosis, but there is no need to worry if you aren't experiencing any other symptoms...

It was probably just a spider bite. 🙂
During the day they’re nowhere to be seen, but once night falls, they throw a party.

It’s probably just some bug getting you—maybe a spider, a wasp, or even a scorpion.

When you get stung by a bee or a wasp,
you’re looking at inflammation. Now, a lethal
dose of venom for an adult
would come from a swarm of maybe 300 to 500
bees or wasps. But look, it can actually be deadly
if you take a single sting right on the
tongue or inside your mouth and throat,
like if you accidentally swallow a live
wasp or bee while you're eating or drinking.

The lining of your tongue and throat
is super sensitive to venom, so
massive swelling can kick in fast,
which basically shuts down your airway and
can cause someone to suffocate. In cases like that,
people need emergency medical help ASAP,
and they might even have to perform a tracheotomy
just to make sure they can breathe.

Thankfully, though, we’ve got effective meds these days
that can knock down that swelling
in a really short amount of time. If you use
calcium injections along with some sedatives,
that swelling should go down pretty quick.

For first aid, you’ve gotta be careful when
pulling out a stinger—use a sterile needle,
tweezers, or even some kind of forceps
(basically tweezers), which is what you'll
deal with if a bee gets you. You should wipe
the wound with rubbing alcohol or another
disinfectant, and usually, just rubbing some
anti-allergy cream (like Benadryl or something similar)
around the area works fine.

Then, throwing some ice or cold compresses on it
helps kill the pain, but if things start getting
really bad with an allergic reaction, you need
to head to the ER immediately. Also,
it’s smart to always check and wash your fruit
thoroughly before eating it, so you don't end up
swallowing a wasp hiding in your grapes, peaches,
or whatever else.