Child has soft and non-adhesive lump on neck. Sonography shows enlarged parotid gland. How long to wait for regression?

My son(age:13y) has a lump in his neck for about 2,5 month, it is soft and non adesive. It grew more but seem to regress a little (wax and wane?) sonography emax report: Enlarged Rt. Parotid gland has a few hypoech well defined masses ( lymphadenopathy ) with different sizes(27 X 15mm, 17 X 15 mm, 17 X 15 mm, 22 X 14mmm…) chest X ray, abdominal sonogram and all blood test ( CBC, ESR , CRP ,LFT,LDH, TOXO, rubella ..) are normal. . In CT scan with injection: Rt. Parotid shows a 18x16mm mass lesion with enhancement. This is an intrinsic mass. without anything more .FNA report: slides show cellular containing a hetrogenous population of lymphoid cells mainly composed of small lymphocytes mixed with medium and large lymphocytes. Many tangible body macrophages also noted. DX: lymphoid tissue with morphologic finding of reactive lymph node, negative for malignant cell I know that FNA is not very precise and the mass dosen;t seem to regess by now. How long wait for regression? I am really worried and don’t know what to do.