nothing wrong with Fast Fret: simply it's not an oil for wood.
it gets your fretboard slippery while you play and it cleans up the fretboard from your hand' sweat when you stop playing, but it does not 'feed' your fretboard.
i highly recommend you to get some good oil, you'll find it in a store for house stuff, dont know how you call it.
or better, those Dunlop 01 and 02 oil & prep, they're simply wonderful. you'll find them in a decent guitar shop.
to clean the strings, i use Dunlop string cleaner, i put some in a rag then i wipe it back & forth under each string. Dunlop makes wonderful products, definitely.