Why is so hard going back to work after vacations?

Last week I started working again, it was worse than I could believe. More than 250 emails were waiting for me to reply them. It took me 2 days to catch up with the emails. The few things that my coworker and sales manager did of my tasks, they didn't finish them or did with mistakes. Those mistakes cost 1500 dollars to the company. Another coworker told me that the guy who repleaced me while I was on vacations left the office to do personal things many times during that week. I knew it was going to happens and I also warned sales manager about it. But who cares?

On Tuesday I remembered the tasks I was working on before to leave for vacations. I should calculate sales commissions to pay to our sellers but I could not start doing it until Thursday and I still don't finish it. I spoke to my boss about the mistake they did on my payroll but she said the salary I was getting was lower than I think she paid to me. I'm sure she is wrong, in fact she could not tell me exactly what salary she thinks I earn every month so we deal that from now my salary is the number that I thought it was plus commissions. I'm not happy about this, she did a mistake and made me lose money on February so I decided not to rush working so hard as I'm doing. This is the problem with working for an old person, sometimes she has no idea what she is doing and she forgets things easily. 

Tomorrow I start new shift. I'll start working earlier and leaving earlier too . I'm actually the only one who can do that. This will be great on winter because I'll leave work when there is still daylight.