My first all grain was an ingredient kit I got from a mail order place. Even though I tried getting icepacks, the yeast wound up being too warm. Having never used Wyeast, I tried it anyway and wound up with the same problem. Since it did seem to ferment a little, I tried racking to secondary and then make a starter out of the spent trub. It really woke up in the starter! I've since read that you can get contaminated strains of yeast that way......I certainly wouldn't culture the spent yeast, but waking it up did seem to get my gravity down while fermenting in another container. Did you oxygenate the wort before pitching? You may have already had enough fermented beer for an offtaste oxygenating now....but I have also oxygenated while repitching yeast (if the gravity isn't low). 1.020 may be too low for that: maybe pitching fresh yeast with starter could be a ticket.