Brake light is now on.

The other day I was backing up and there was a boom-like sound and it seemed like I backed over something. At first, I thought I blew my rear tire. Nothing appeared out of order. Today, the boom and bump-like feeling happened again plus it seemed difficult to get my car to advance--I had to give it some gas, plus it seemed like my brakes suddenly changed--I had to press further down to get the car to stop. Just as I'm pulling into my driveway, the brake light came on. When I got out of my car, it smelled awful, like burning SOMETHING, maybe rubber? I can't imagine that my brakes are shot--I have my car serviced regularly and they would tell me if my brakes need replacing. Any idea what's going on? Thanks.