Advice please

This is a game I was doing well in despite a couple of blunders.  I was doing well into the middlegame then my game went south, any insight is appreciated.

i think by retreating your queen you lose alot of tempo.

I believe it is strong to play Qa4 and sometimes Qd3 is strong as well.

I may be wrong.

Retreating the queen is questionable.

Also, you lost your center pawns pretty quickly. You probably moved the wrong knight on the 6th move (in a hurry to castle)? Once he grabbed control of the center, he just slowly took over everything else.

Aight, first thing you need to do (I'm guessing this wasn't a blitz game) is to take your time and look around for each move. Think about the position: "Can I take that piece?" "Who is defending it?" "What will happen after I move here?" etc. Watch the entire board, as there could be a piece on the side that you didn't notice. Even when your oppenent seems to have blundered, there may be a trap.

In the opening, watch out for moves that will get your queen out too early, unless it is worth it.  Consider the pros and cons. For instance, when you played 3. Qxd4, there was no need (after 1. e4 c5, you could have played 2. Nf3, preparing to play d4 later). This doesn't mean that you should never bring out the queen in the opening. For instance, after 6... Nxe4, you could have played 7. Qd5, both threatening to take f7 (which would be checkmate) and threatening to take the knight. After 7... Nd6, defending from both threats, you would have been able to take the e5 pawn with your knight, thus reclaiming the center.

Other than this, the only other advice for improving that I can give you is: practice.