What Causes Pea Sized Lump In The Groin Area During Periods?

I ve been getting a pea size lump in my groin area around the time of my period, tender to touch and usually goes away or down in size after my period finishes. Sometimes I don t get them at all. It usually happens in the same place. I ve mentioned to my primary doctor during my annual physical and he says that it s probably a swollen lymph node...I ve spoken with my dermatologist and he says it s hormonal and a cyst...I ve spoken with my gynecologist and he thinks that s it s endometriosis since it occurs around the time of my menstrual cycle? All the doctors don t seemed concerned? Although I am. Which one is it and should I be concerned? Sincerely, confused patient.