sounds like my sort of field,
try this:
remove the fuse and put a multimeter (dc amp mode) probe on each side of the fuse holder and see how many amps are flowing through the circuit, if over 10A obvesley is gonna blow
remove the fuse and put a multimeter (continues mode) on a ground somewhere under the dash and probe each side of the fuse holder if it beeps theres a dead short in the accessory line somwhere
to try fix this do u have a aftermarket headunit?
or anything fitted anything electronic in the last week or so?
its ether a short, overload, faulty component, or bodgy install
im in north syd if u want me to check it out 4 ya (send pm)