I just wanted to write an update and say thanks to everyone who gave me advice on my post last week!
I called my student health center on Monday and made an appointment, and they got me right in. The doctor there was okay. She made one annoying sort of slut-shaming comment (said "good for you!" when I said I'm not sexually active...) but was otherwise fine. She was good about being very matter of fact and keeping me covered up as much as possible which was helpful. I found the suggestions to just detach myself from that part of my body very useful. The doctor found the lump without me telling her where it was and was quite concerned (especially given my family history), so she referred me to get an ultrasound. I went in for the ultrasound on Thursday and the radiologist said she didn't see anything at all. So, yeah, that was the end of that. I'm still a bit nervous, because I can still feel the lump even though the radiologist said nothing was there, but they said to come back for a follow up in six months. So I figure if it's still there in six months, they can do another ultrasound and check on it. In the meantime, I feel much more at peace about it, so thank you all pushing me to go to the doctor, and for your helpful advice about dealing with the gender issues!