Whey would be high in sugars and acidic. I don't see any fertiliser value in it at all!

I don't know what sweet whey is, but whey can be used, sparingly, watered down, around acid loving plants, but its not a fertiliser as such - it simply acidifies. Since tomatoes prefer a ph of around 6.8 (7 is neutral), in common with most (though not all, some prefer alkaline) vegetables, I wouldn't call them exactly acid loving, so a better use for your whey might be to add it to your compost heap. More info in link below, but its not scientific

http://www.vicariouslyvintage.com/2012/09/21/17-uses-for-whey/