I've had taccycardia for over a year. Could this be a pulmonary embolism?

Not really. A pe would present as cough, bloody chest pain, and shortness of breath. Now, it could be associated with tachycardia in an acute situation, but you're talking about a year of rapid heart rate. I'm assuming you've been seen and evaluated by a physician.If not, do so. Good luck.
Possibly. While some patients do have something called chronic pulmonary embolism, the odds of having that without ever being diagnosed with DVT are small. You should be discussing this with your doctor so they can work you up for other causes as well (hyperthyroidism for example).