2005 Kia Spectra Room Fuse keeps blowing.

I have an '05 Kia Spectra that has started blowing room fuses. Started last night was driving, and the radio, clock, interior lights, basically everything associated with that fuse stopped working, but not all at once. It sort of slowly went out. When I got home I replaced the fuse, and everything seemed fine. In the morning I got in the car and the radio and everything was working fine. As soon as I got where I was going and turned the car off, it blew again. I only know this because when I tried to lock the car the power locks didn't work. When I got back to the car I tried replacing the fuse only to find that as soon as I plugged the new fuse in, it would blow. This happened 3 times, and I finally gave up and decided to just live with it for the time being. I really would like to fix this, but I have no idea what it could be. There's an after market radio, but it was professionally installed, and quite a while ago. Also, the fuse that was installed initially was in a plastic "shroud." I couldn't get the fuse out, so when I replaced it, I didn't use the plastic "shroud." If this is what caused the problem, and I doubt it is, I need to know how to get the old fuse out.