Y r my female guinea pigs fighting?

i have had my flo rida my first guiena pig ever for a little over a month now! i LOVE her! yesterday i just bought another female guinea pig. i tested them out this morning and put them together. at first they nibbled at eachothers s which i didnt get give me some info please! and then i put them together again and they fought BIG TIME! they are both rosette and htey r the same age! i didnt put them in the same cage. they were on the living room! wat is going on y r they fihgting like this and will it stop???: help me!!!!!!