By your description, you have pars interarticularis fractures at L3 bilaterally but one has healed. How was the healing diagnosed? Was it by X-ray or by CT scan? Did you have an MRI of the lumbar spine? Pain can be generated by a unilateral pars fracture but can also occur from a degenerative disc caused by the instability of the fracture.
Where is your pain? Do you have back pain or leg pain or both? When does the pain occur- with standing, sitting, lifting or? You need to supply more information.
Your lowest vertebra with the “wings joints” is a transitional vertebra and the “wings” are transverse-alar articulations between the transverse processes of L5 and the ala of the sacrum. These articulations normally stabilize this motion segment and cause no pain.
The possible tumor at the base of your neck is another matter entirely and needs to be followed by a neurosurgeon if it involves the spinal cord and by a spine surgeon if it involves the bone of the vertebra.