What Causes INR Level Of 1.4 Even After Increasing Warfarin Dose?

I have been taking Warfarin for the past six years and the range has always been between 2.0 - 2.5 I also enjoy a glass or two of wine with my evening meal. however my last two INR's have been 1.4 even though after the first reading of 1.4 my medication was increased slightly. The only change to my lifestyle has been that I did not drink any alcohol for three days prior to each of these blood tests