I'm on warfarin. if my blood is too thin (3.9) can it make me fatigued?

Possibly: Although fatigue is not a common side effect of Warfarin and the viscosity of the blood is not affected (no such thing as thin or thick blood just normal or prolonged clotting time) I have noted a number of patients who experience a feeling of fatigue with the drug irrespective of the INR level. You might be one. Certainly the diseases requiring anticoagulation can often cause fatigue as well.

Usually not: The main reason for fatigue in this situation would be if the high INR were resulting in bleeding and your blood count were low. Therefore, that needs to be checked, along with stool for blood by your doctor. Rarely, a coexisting liver condition could cause the INR to be difficult to regulate, while separately causing fatigue, so would also check liver function. Good luck!!

Fatigue: Pretty high INR,check with your doctor Fatigue could be from this