[Programmatically-psychological question]

Hi,

I am a programmer. I work in some computer science company and I finished Master of Science in Informatics on some rather good university. Since the beginning of my career I had some problems with debugging complex problems. It is no problem for me to create some rather simple program (for example I implemented Dijkstra algorithm in Unity 3D and I co-operated with some people to create some game-prototype during Global Game Jam few days ago).
But when it comes to debugging I have much problems, especially in analysing the architecture of very big systems. Now I am working for 1,5 year in some computer science company. The application I maintain has about 5 000 classes of code - only talking about part of the application I maintain in my team and this app is written mainly in C#, so I use Visual Studio 2010 to debug code.
I know basics of debugging in Visual Studio rather good:
Debugging with Breakpoints: Step Over, Step Into, Step Out, Continue, Set Next Statement, Show Next Statement, Conditional Breakpoint, Watch Windows, I know how to use call stack to see how the code goes from one method to another.
But anyway this whole application is so complex it is hard for me to fix issues I am assigned to. Other people in my team somehow fix defects in this application. It is rather long time and I am worried about my efficiency in debugging, which is very low, especially comparing to others. This causes stress that I sometimes try to reduce by meditation (very rarely, let's say 1 time for 2 weeks) and accepting my emotions, but still stress reduces my effectiveness very much (when I am stressed it it very hard to focus on work). I have also problem with concentration on my work (which other people from my team have too, because they sometimes for example use Facebook etc. - but they can focus on their job much better than me).
Debugging in much simpler for me when I work on small projects - for example if I see a bug in my own rather-little project - I am able to debug defect in rather short time. But the complexity of application I now maintain and my knowledge about it is limited.

Can you give me some advices how to deal with my low efficiency in debugging? You can of course talk about various ways to deal with this (psychological, computer science, diet etc.)