I need memroy stick help

I am not good at technology but i have this 4gb memory stick pro duo for my sony camera. The problem is that I can only take 3 picture and the camera says low internal memory. I check on my computer and said that the disk only has 15.4mb capacity. I tried to format it but it does not fix it.

Any advice will help, and thank you.

For some weird reason the disk fixed it self. When I looked at my camera last time it only showed three picture of 11mb and so did my computer but when I hooked up the camera to one of my old computer all the picture showed up again. Then the camera showed that I had 4gb of space when few days ago only showed 15mb. Weird.