Multiple columns in mobile devices turn into one column

I have a responsive disign for a website and the only problem I have is that for mobile devices, eventhough I have two columns in the design, in real live it just shows one column, doesnt matter if I put two, three, columns, in mobile, I just get one column. For large and medium devices it works well, I can use as many columns as I want, but not for mobile, does anyone have had the same problem?