I'm not feeling very well so why are my legs hurting? Is it the flu?

I had bad allergies yesterday but my legs were not hurting. I still have the allergies but it's clearing the way and now coming up with the cold and my thighs are hurting. They've been hurting since this morning I don't know why. I really don't want to miss the concert tomorrow they're going to with my friends.
I'm not feeling very well so why are my legs hurting? Is it the flu?
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