A lot of water condensation is a symptom of too much humidity inside.
Do you have a humidifier, either stand alone or furnace mounted adding
moisture?
Having one that is set too high will definitely cause problems. If
it's just happening
on one window, it might be a bad window seal, but that should be
obvious as moisture
shows up between the panes. If it's happening on most windows, then
there is too
much moisture in the house and it has to be coming from somewhere.

For the bathroom fan, adding insulation around the vent pipe should
help, as it
will keep the cold attic air from directly reaching the pipe, so it
should reduce
condensation. Also, make sure it's vented correctly outside and not
directly into
the attic.

In any event, you need to get this resolved because a lot of
condensation can cause serious
problems. It's also getting wet where you can't see, behind wall,
around recessed lights that
extend into cold attic space, etc.