Seems likely the two load lines from the GFCI go to the light and the
fan, just going by numbers. In that case you might have to run a new
wire or two. Here are some options if that is indeed the setup (source
to switch to GFCI to fan+light) -- which one is best depends on how
easy it is to add a new line to each place:
1- Can you just swap that GFCI and the switch? In my bathroom, the two
happen to be right next to each other (well, one right above the
other). This would give you source to GFCI to switch to fan+light,
which is what you want.
2 - Run new lines (or just one new line) from the switch to the fan and
light. Then obviously disconnect the load lines on the GFCI.
3 - Run a new line from the source to the GFCI, and just connect the
three other wires in a pass-through configuration in the GFCI box. You
probably don't have room in the GFCI box for this though, unless you
can get rid of those other connections that would be in there. Maybe
you can get an extra deep box? Seems annoying.
4 - Use the old 2-wire switch-to-GFCI cable to pull through a new
3-wire switch-to-GFCI cable. Then you can run the white as the neutral,
black as always hot, and red as switched hot. At the GFCI, the outlet
LINE screws get the black and white from the switch. The red from
switch connects to the black from fan+light. The white from switch
connects also to the fan+light. Nothing connects to the LOAD screws.
Unless there are other outlets in the bathroom that are fed from there
already, in which case you could put those on the load screws.