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It would be a good idea to rule out deep vein thrombosis
as a differential cause for cellulitis
. From your description it appears to be more probably Cellulitis, but i would like to rule out Deep vein thrombosis, as cellulitis won;t last for a month if proper antibiotic and limb rest is given. Next time you have swelling kindly get color doppler scan done to rule out thrombosis.