Help please emergency! ?

okay so right now i'm scared or idk wat going on but about 2-1 months ago i took a photo and i took one today and i look fat! idk why and before i was a size 14 now im a size 8-10 and every one tells me i look thin and all but i feel so fat and when i look in the mirror i look fat even tho people tell me i look supee thin and idk why this is happening i need help im 13 years old, and im a girl and idk y and every one says my face is,skinny and small but i look in the mirror it look chubby and round help!!! i'm driving nuts! even my friends say everytime i see u you look thinner but for me it everytime i see myself i look fatter