Hello, I Have Been Having A Swollen Inguinal Lymph Node

Hello,
I have been having a swollen inguinal lymph node for 6 weeks. It is not painful but tender. It looks like the size of a golf ball. The doctor first told me to watch it for one month to see if it goes down. I felt like it went down and swelled back up again. I noticed that it swells up more when I'm about to get my period. I did std tests and blood tests and everything was normal. She told me that it looks like it's 3 lymph nodes that are swollen. I keep checking it. Does that make it bigger?The doctor just recently prescribed me with antibiotics. If it doesn't go down she recommends a biopsy. I am really worried that it could be cancer. What do you think?