Elevated ALT Liver Enzyme

I am a 27 year old male that drinks alcohol more than average, but not at alcoholic levels (probably around 15-18 drinks per week).  I have had 5 blood tests in the past 9 to 10 months for various reasons (insurance applications and follow-up with primary doctor), and in each test my ALT liver enzyme has been slightly elevated near the low-to-middle 60s (72, 54, 62, 64, 68, respectfully).   All other blood tests are normal, including all liver function tests (AST is always around mid-20s) and others (cholesterol, glucose, thyroid, etc...).  It has not caused me problems when obtaining life insurance or disability insurance and my doctor is not worried at all.  In fact, my doctor specifically said that he is not worried because I display no symptoms of liver disease and my ALT is only slightly elevated.  Also, it should be noted that I did not have any alcohol for three weeks before taking my last blood test, which resulted in an ALT level of 68.  

Finally, I should also mention that I am 5'10 and 165 pounds.  I am not overweight, I run 3 miles four times a week, eat moderately healthy, and have a lot of energy.  I have really never been sick in the past or diagnosed with any allergies or illnesses.

My question is, should I be more aggressive with my doctor and request an ultrasound and more follow-up tests or just follow his recommendation and get re-tested in 6 months and see where my ALT is at.  

P.S.  I plan on completely abstaining from alcohol for 5-6 weeks before my next test.  

Thank you in advance for your answer

[MarkTPease]

Stop the drinking!  15-18 drinks per week...duh!  Try none for six months and watch what happens with your liver count.  It was cool when you were in college it will now catch up to your body.