Hi Mary,
I hear your concern, and these are easy to come to us when we feel a lump because it can be such a variety of things that made the lump appear.
From what you described, it seems like it could be in the area where there is lymph nodes. You mentionned you sweat a lot around there because of your cycling classes, it may be related to that.
If it is a lymph node, often they will swell because of an infection and trust me, it doesn't need to be a major infection for the lymph nodes to react! A cat scratch, a nick from shaving, etc... see what I mean.
Around that area, there is always also the possibility of an inguinal hernia.
Might be something else too...
So I would say that your best bet is to take an appointment with your family doctor. If it is an hernia, it is better to get fix soon, because of the risk of strangulation(lack of blood circulation etc...) and if it is swollen gland, then most likely the doc would give you anti-biotic to see if it clears an infection. Might investigate further if it raise concerns.
I would also say to keep an eye on it but to play around with it as little as possible!(keep track if it get bigger, decrease in size, change form, etc...)
Hope it turns out to be nothing serious!, But remember, better be safe than sorry, right!!!
Take care!
Tekkymrc