…while it has been some time since your initial post I have some information that may help for those in the future. My background: Emergency Physician for over 10 years, BS in Exercise and Sports Science, and I race road/cross.
Some definitions first: A nodule is a firm mass of tissue that is easily palpated and has relatively decernable location (think a marble under the skin). A cyst is a fluid filled sack (usually non-infectious like a water balloon) while an abscess is similar to a cyst (fluid filled), but that fluid is bacteria and byproducts of cellular breakdown (infectious). Induration is firmness of the soft tissue, and ulceration is loss of the top layer(s) of skin.
The perinuem is the space between the back (posterior) aspect of your genitals (scrotum or vulva) and the beginning of the anus.
Swelling in the area can be from a multitude of problems but the most common is going to be some form of induration and/or slight ulceration from either ill fitting shorts, poor fit, poor hygene, or inappropriate lubrication (most likely combination of all). This is most easily avoided by addressing the aforementioned causes, rest from the bike seat, and allowing the tissue to heal. A bad ulceration of the area would be a “saddle sore” although this term is ambiguous and used freely to describe pretty much anything wrong the area.
Next on the list (if you continue to cycle) is going to be the formation of an abscess. As the skin surface is broken down (ulcerated), you have lost your skins protective barrier against bacteria. Bacteria in the area gets below the upper layers of skin and form a small pocket of pus (abscess). In an effort to “fight” the infection your body creates an immune response that causes swelling, significant pain, and induration to the area (similar to a giant zit). Abscesses need to be opened by scapel and drained the vast majority of the time. Very rarely will they get better with just antibiotics. After draining, you’ll need to rest (1-2 weeks off the saddle), and once again address the issue of fit, bibs, lube, etc.
Next are several of the uncommon in the literature but more common than you think issues. Ischial Hygroma/Cyclists Nodules (perineal nodular induration - PNI). A hygroma is a fluid filled sac (similar to a cyst) that occurs from multiple micro trauma to the area, and usually is secondary to a poor fitting position and saddle. These are lumped into the same category as Perineal Nodular Induration (Cyclists Nodule, Bikes Nodule, or “third testicle”). The downside of Cyclists nodule is that you can try a steroid injection which may decrease the swelling, but the actual fibroblastic spindle cell tissue mass stays in place and can recur… so the recomendation is for resection. For further reading see here: https://www.ajol.info/index.php/sasma/article/viewFile/184227/173599
A firm nodular mass on one side of the perineum (marble under the skin) that isn’t significantly tender but rather an annoyance and mild irritation think more along the lines of Cyclists Nodule. This would be need to be addressed by your Urologist, a good colorectal surgeon, or a good gen surgeon.
On the other hand, a red, inflamed, very tender mass that dosn’t have very defined edges is more likely abscess/cyst and can be drained by any good primary care physician.
I hope this helps. I wish it was as simple as “swelling = do this”, in summary it’s a bit more complicated. Last asterisk to the conversation, there a many other things that are much less likely but possible, see your doctor for further evaluation.