For vancomycin why check trough and peak. What does low or high trough and peak mean?

To know correct dose. The levels of vancomycin in the blood are not accurately predictable based only on the dose given. The peak level is to make sure the dose isn't too high and the trough to make sure it isn't too low. These tests are especially important if there are kidney problems. I'm sure your doctor knows what she is doing, but if in doubt, ask for consultation with an infectious diseases specialist.