changed location? (different house / room)
could possibly be power / interferance.
are you usine a generator? or "al-pesek" before the amp?

if you feel comfortable doing it, I would open it up and look at the electronics.
I don't remember how accesible they are in Strats, I think you can reach them without taking off the strings.
if the wires look ok, you can check with a multi meter to see that there are no shorts
and the pots are behaving normally,
and finally you can bypass the pots one by one to see if they are defective.

if this isn't your cup of tea, take it to someone...

and most importantly may you and the guitar feel well soon!

edit: can you upload an audio file?

what ravitz said.