How many games should one play online per day or week? I participated in a tournament on chess.com and I have to play like 12 games, 3 days per move, although it's plenty of time, I can't concentrate, I noticed that when I play many games, I lose because I make mistakes.

The thing is when you have 12 games to be played, you often find yourself, not playing at all or playing all the games simultaneously, to just get over with it, and do something else other than playing chess.

So in an ideal situation, what is the best number of games to be played per day or week for average users? 

A side question, is it good to play such tournaments? I mean when you have many games to be played, you'll lose concentration (at least I do) so isn't it better to play live tournaments (15 or 30 min for each player) isn't that a better way to concentrate on the moves?
Since playing chess is not a job for most of us, it may not make much sense to ask how many games should you play. Some people relish the adrenaline rush of 1 minute chess, some can play for hours, some like to play three games at once... and then some others like to play once a week. The answer depends on who you are, but since it seems that online tourneys stress you out, it may be better for you to attend live ones.

I know this is not much of an answer, but I think it is closest to the truth.