breaking problem

[turbocharge32]

I didnt know where to post this but i hope this is ok. I have a 2000 mustang convertible i bought at the end of february. Everything ran fine until about a little over a month ago. One day i rolled through a stop sign. It kept getting worse to the point where it does this daily. It doesnt always have problems stopping but it does daily. Im the only driver but i took it to a shop for the brakes to be looked at. They said the brakes and everything with them were fine. I left and had the same problem. My brother and dad both drove it but said there was nothing wrong. I no there is something wrong because i have never had a problem with it. When i stop i have to push the brake harder then i ever did before and sometimes almost to the floor. I have to brake a block in advance to i can stop correctly and i dont fly up to the stop signs. At the one stop light we have in town sometimes when im completely stopped it will start moving for no reason and i have to push even harder again. There is something wrong and i dont understand. any suggestions would be helpful..thanks!