What Causes Elevated Liver Enzymes After Taking Bactrim?

I am 7.5 weeks post-kidney transplant as a result of PKD. All my labs are normal except my liver enzymes went up dramatically this week. I started Bactrim last week (just one dose). Doc told me to stop the Bactrim and take Vitamin D (2000 units a day) and repeat labs in a few days. Should I be worried? I ve never had a problematic liver test?