Underweight, low blood pressure, fast and slow resting hbr, achy legs and arms, breathless with stairs and dizzy spells. is it my heart?

Don't know: It could be your thyroid, an autoimmune disease, just your heart, a lung/heart circulation problem .... See a physician and get to work at getting to the bottom of it.

M.D. visit: A first step in the management of these symptoms is to have your cardio-pulmonary condition assessed. Pulmonary arterial hypertension should be considered in the work up.