What Could The Raised Freckle On Arm That Has Changed Color Be?

I am a 20 year old female college student. i have several freckles on my arms that are all flat and light brown that do not change color or shape. however, i recently noticed one of my darker freckles has now become raised. so much so that i though i had a bug bite which would be unusual because its cold here. i didnt look at it because i have been wearing long sleeves due to the cold. its very tiny but has become raised and itchy and had gotten extremely dark in color in the center. the skin around it also looks dark, like a bruise almost. and it is tender to the touch. not too long ago, this was just another flat lying freckle that i've had for as long as i can remember.