What Causes Frequent Foot Cramps With Bruising And Swelling?

hi, im a 16 year old girl.
and these past few months, i have had cramp in my foot at very random times. the first time was when i was walking home from school, it just started randomly and it was very painful. it has happened many times since then. and last night, it was so bad that it woke me up, and it my foot was all bruised and swollen on the side. it was extremely painful, and i do not think it is just normal foot cramp? help?