What exactly makes a day bad?

I did promise one more post, eh?
The other thing I wanted to talk about is what constitutes a "bad day" at my job. Yesterday was a bad day. Here is what made it bad:
- I spent an hour in the morning trying to sort out an issue in which an interpretter who was scheduled to attend an exam had to cancel last minute. This process consisted of me making alternating calls to our scheduling department and a very irate claimant who did not understand why we could not call every random interpretter in the state of Ohio to see if anyone was available instead of rescheduling the appointment.
- People just kept calling in. I would start to do something and get interrupted five times before I would give up and move on to a simpler task.
- Late in the afternoon I took a call for a coworker who was gone for the day. He was lucky he was gone and he owes me big time for taking the call. It consisted of a client that that clients father. The client was alleging learning disabilities. I needed to get a lot of information about treatment, daily activities, and willingness to attend an exam. It was one of the unfortunate and all to common cases where it is obvious there is a genetic connection between the clmt and their parents, in that despite being the "responsible party" so to speak, the parent is not capable of answering most questions or even holding a normal conversation because their mental status is so impaired. It was a long call and I got as much information as I could, but it was very frustrating.
- I found mistakes. When you have 150+ cases, even someone who is good at the job will make mistakes, and as a rookie I make slightly more. Yesterday I found a case that had been going on since March that appeared that I had wasted quite a bit of time pursuing records that had not come in. This means the case will be delayed even longer because my over-optimism about source cooperation means I did not schedule an exam as early in the process as I could have. Finding a case like this makes me feel guilty and worried and puts me in a bad mood, even when I am told time and time again that it happens and cases slip through. It is not something that bothers me all of the time, but when I do encounter it I always feel like I should find a way to do better.