Fatigue & tachycardia from talking. doc says not heart or lungs. endocrine? autoimmune? clot? what to test? neck & scalp pulsate, unsure if related

Many possibilities: Fatigue and tachycardia while any activity like talking is non-specific and can be due to a range of problems. The first thing would be to document the extent of the tachycardia - you could use a heart rate monitor from any vendor. Knowing that your mean heart rate is elevated over a 24 hour period is the first step. Obviously you have fatigue and excluding endocrine problem is the first step.