Where did I go wrong? QGD loss as black

The exchange variation with Nf3 is harmless because can solve white square bishop problem with 6...Bf5 or possibly 6...Bg4. Don't think including h6 helps much. The point of h6, as I understand it is to follow up with Nh5, or if haven't 0.0, g5 then Nh5, to  exchange Bg5, and get two bishops. (You did eventually do that on move 19, after a few not very to the point moves by both sides).  The usual idea of playing the knight round to e6, is to follow up with g6. Ng7 then Bf5 to solve white square bishop problem. This is problembatic with h6, because Bxg6, and Qxg6ch could be strong. Other cases where h6, doesn't help is when play third rank idea with Re6 to defend c6, and to be able to play rg6, rh6 to support kingside attack. If that plan with Ne6 not viable then Nd6 is more often a better square for knight.  Otherwise played a few pointless moves like bd7, it is arguably better on Bc8, and Bf6, were it was better placed on e7, if white plays b5, then bxa3 possible. Both sides "oscillated" for no obvious reason i,.eBe7, bf8, Be7 and Ne6, f8, e6.

It would help to learn the typical plans to face minority attack. For example a typical one is playing b5, then nb6-c4, with a5, and a5xb4. 

The standard way to counter the minority attack in the QGD is to counter with f5

I think black is guilty of generally timid play here.  White had all the time it needed to set up the eventual queenside push (though the open h-file, especially after the exchange on f3, looked like a good line of attack, too.

Once you were down a pawn or two, you needed to get the rooks off, and keep the bishops on.  He had 2 pawns on you, but one was a doubled pawn, a draw black should be able to hold.

It doesn't matter how good a defensive formation is, if you give a player of that level enough time, he'll usually find a way to pick it apart.

I didn't know that.  Thanks for mentioning this move.

My personal experience playing with both sides is that black playing ...h6 early on seems to be bit of a loss of development time. Often black counters with a piece attack on the kingside, like in this game link:

Exactly. He doesn't seem to know the basics of this opening.

After white goes for the exchange variation, you want Bf5 if possible. You also want to play a5 because then after white's move b4, you get the a pawns off the board, so even the worst case endgame is not a forced loss

Also, as he more or less points out, you're mixing systems. h6 didn't makes sense in your game.

Another idea of Ne6 (other than Ng7 with Bf5 as he mentioned) is that Ne6 protects d5, allowing you to sometimes play c5.

 The OP mentioned saw 6 ...h6 recommended somewhere, and it was probably this review of "Chess for life" https://www.chess.com/blog/IM_Kgwm/book-reviews-my-interesting-reads-this-summer-part-1.

6....h6, avoids the endgame after 6....Bf5 7.Qb3 Qb6 7.BxN QxQ 8pxQ pxB although it doesn't look that terrifying.