What you are describing sounds very suspicious for gout. It will give you a very swollen, painful, red foot without any history of trauma. The diagnosis is made by exam, but a blood test for uric acid can help (it should be high). If it is gout, colchicine and possibly steroids will help.
Shingles shouldn't give you a very red foot - it should just be a few red spots. Because of this, I think shingles is unlikely.
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I'm glad to hear that gout was ruled out, although this can not be ruled out by lab testing.
Infection, like cellulitis, would be the next diagnosis to consider. Perhaps you were bitten by an insect at night that got infected. It would be reasonable to start antibiotics like Keflex and see if the symptoms resolve. If not, you should get a lower extremety doppler to rule out a clot in your leg vein, but this seems unlikely.
I wish you well.
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