My husband has had a fever and severe upper leg pain for the last 24 hrs. could it be an infection that is causing this?

Seek help.: Fever and severe leg pain for 24 hours could certainly be the result of an infection. There are other ominous causes too, like a blood clot (DVT) which can cause sudden leg pain. I highly, highly recommend you call your doctor today. He may even need to go to the er; it's hard to tell based on your description, but regardless, he needs help.