I've been very jittery recently and when I took my pulse it was 120 per minute. I also have a slight lump in my neck. A friend suggested my nerviness might be due to thyroid trouble.

Is this possible?

Certainly. An over-active thyroid is associated with jumpiness and a fast pulse. But you could just have an anxiety state. See your doc. She'll examine you, and probably arrange a blood test to find out how your thyroid is functioning.