My legs sometimes feel numb and have blue blackish spots, what can cause this?

I have two big spots behind my legs that are blue blackish and my legs sometimes feel numb what is the cause of it I didn’t hurt it and I’ve been feeling it like this for a week and sometimes it changes to the other leg.. sometimes it get really numb and I don’t feel my leg at all.
Age:24
Female
Medications: None



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