Need help with a lyric

[SicilianMother@xxxxxxx]

I have this lyric, or part of one, that I can't remember exactly what it is 
or who wrote it.  I am pretty sure it is NOT a Who song lyric, but if anyone 
could help......

The lyric is something like:

"I wish I knew then, what I didn't know now"   or
"I wish I didn't know now what I didn't know then" or
"I wish I knew now what I didn't know then" 

Something along those lines.

It's driving me crazy!!!!

Thanks,

"What the fuck am I trying to say.............n...n...nevermind"
Ozzy Osbourne
Jo