Elevated liver function - can I trust my diagnosis?

I am a 50 year old female with Type I diabetes for 20+ years.  Relatively few complications.  Mildly low thyroid.  Good control of diabetes, normal weight and avid exerciser.  General good health.  Late last year had three slightly elevatedd AST and ALT tests.  Doctor did ultrasound, heptatits tests and a variety of others including lupus and auto-immune liver disease.  All tests negative.  We waited three months and repeated the AST and ALT tests and they had returned to normal.  He has told me to forget about it, that we will likely never know what caused it.  I normally drink one alcoholic drink per day (stopped during the testing but have since resumed) and do not take herbal supplements, vitamins or tylenol.  I'd like to "forget about it" but wonder if that's the best course of action.  It's been 60 days since the normal test results.  Should I ask to be retested?