Thanks for posting your query.
As such there is no Eustachian gland in human body but Eustachian tube is present.
With the available described symptoms, there appears to be possibility of upper respiratory tract
bacterial infection with localized draining lymph
But with time and prolonged use of antibiotics, these lymph nodes gets fibrosed and that's why size is not decreasing.
You should consult with internal medicine specialist/ ENT surgeon and should go for thorough check up.
You should go for excision biopsy
of lymph nodes for exact diagnosis.
You should also go for throat swab culture and sensitivity.
Take proper antibiotics according to culture ans sensitivity reports.
Dr. Mayank Bhargava