Analysis needed
I believe that going into the exchange (12... Nc6) was a large fault in your pawn disadvantage. Although it seems equal, when coming out of the exchange, either the c or h pawn would be lost, and your a pawn became isolated and hard to protect or make use of.
The exchange essentially lost you (maybe a little more than) two pawns. Better move may have been (12... a6) kicking the knight away.
I also felt that your opening play was perhaps slow? By move 8 you can see that white employed both knights, their bishop, and queen while you have only your knight, bishop, and single pawn mobilized. tubebender
** I'm a little new to chess, but I've studied a bit. Still, I'd take my revision quite cautiously. :) **
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