I found it........ finally. It turns out that the relay was heating up enough for the breaker to shut down the circuit. I switched the relays around to try and find a faulty breaker, as someone suggested, but they all seemed to have been okay. Then the situation got worse...... the windows and the radio wouldn't work at all. I replaced the relay for the windows/radio and left the fuse cover off. Now it doesn't heat up and the breaker doesn't trip, so it's worked so far. About a week now and it works fine.
Thanks everyone for the help.