Pulmonary Embolism Support Group
By far the most common form of pulmonary embolism is a thromboembolism, which occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. Symptoms may include difficulty breathing, pain during breathing, and more rarely circulatory instability and death.
I'd stay if your INR is in range and stable (1.9 isn't very low) chances are it's not a clot anyway, whether it's likely to form in the lower arm or not. But if it's really concerning and you're not seeing any improvement, you may want to get it checked out although since you're on warfarin not sure what they'd do for you if it was a clot.