Can jak 2 positive. Polycythemia vera cause chronic low grade fevers?

No. Pv by itself does'nt cause low grade fevers. However, pv can increase your risk to have blood clots and blood clots can give you low grade fevers also, pv can transform into other condition i.E myelofibrosis as well as mds/ acute leukemia in about 20%-30%). Low grade fevers occur quite commonly in myelofibrosis and acute leukemia. See your md to rule out other condition i.e. Autoimmune , infection.