The enlargement of lymph nodes may be due to infection, tumor, drugs reactions etc.
Each group has a long list.
Infection may be bacterial, viral or fungal, protozoa etc.
Among tumors besides lymphoma, there are many other tumors can cause lymph node enlargement.
Proper medical history both past and present illness, thorough physical examination along with stepwise investigations are needed to come to conclusion.
You should contact an experienced Internist who can throw some light and guide you in the definitive way.
Though your previous reports are normal, you need repeat tests along with others according to the examination findings.
Hope your early relief. Regards. Dr. SS