I have a lump under my armpit..?

If you look at it its about the size of a quarter but if your feel it it small.... I just noticed a couple days ago but it couldve be there before tht.. I kinda sweat alot under there since it summer.. I'm 12 and its my left arm... Is it cancer!!!?? Sorry if I'm over reacting... And also I felt something around my armpit about a couple months ago its about the size of a pea and I think it was a cyst but it went away but I was kinda wondering if it has anything to do with tht.... PLEASE AND THANK U :)