Only way AAS would effect lymph node size is by injecting and thus getting a little infection. Do you inject?? If so that could cause it to get enlarged.
Other causes of node in this area could be STD, any local or systematic infection, benign lymphadenopathy, and as mentioned above cancer (lymphoma). Did doctor check your nuts?? Sometimes testical cancer will spread to lymphs in the pelvis area.
If it is still big after a cycle of antibiotics, I would suggest a biopsy to the doctor to rule out the cancer possibility.