History of 4 & 5 metatarsal stress fracture that healed.now sharp grating pain is back. new xray shows nothing acute. now what?

Fracture care: It is very possible that you have incomplete fusion of the fracture site. The diagnosis of 4th and 5th stress fracture seems unlikely typically affects one metatarsal. I suggests that you obtain an MRI to make sure you have the correct diagnosis. Until then rest don't aggravate it.

Possibly unrelated: If the former stress fractures are really healed, the pain may be completely unrelated and from something new. Have a MRI to see if something else is going on.

Metatarsalgia: The fractures may have changed the structure of your gate. May benefit from an orthotic. Other studies like a mri/ct scan may help figure other issues that may have arised.