I'm curious as to why you didn't ask about this when you were checked for STD's since they were already looking, it would have been the perfect opportunity to ask.
Here's a link that might help. In the future, when you have a medical concern, it's always best to go straight to your doctor for any questions. They know you and your medical history so they will know best. Asking random people on the Internet is not always the best thing to do.
http://caredownthere.com.au/_pages/normal_lumps.html