First of all: after 10 years of disease-free life, chances are extremely low that it is a recurrence of your hodgkin. So thats good news.
I assume that you are getting regular check-ups, including bloodwork, x-rays and CT-scans annually?
Radiation therapy does increase the risk of developing leukaemia later on in life, however your peripheral blood film should have indications towards this and i assume your doctor has checked for these. If the lymphocytopenia is severe and you do not feel comfortable about your current situation. I would recommend that you undergo a complete check-up at a department of Internal Medicine.
lymphocytopenia has a wide range of possible causes:
AIDS and other viral, bacterial, and fungal infections
chronic failure of the right ventricle of the heart (This chamber of the heart pumps blood to the lungs.)
hodgkin's disease and cancers of the lymphatic system
a leak or rupture in the thoracic duct (The thoracic duct removes lymphatic fluid from the legs and abdomen.)
side effects of prescription medications
malnutrition (Diets that are low in protein and overall calorie intake may cause lymphocytopenia.)
high stress levels