Possibly Sick Corydora?

[alkamist]

Hello everyone!
I've had my albino corys for around two years now, and I bought them when they were adults (I'm unsure of their exact age, but I'd say around 4-5). They're all very happy, breeding every few weeks, but I've noticed something strange on one of my females. I posted this on Reddit but nobody could help me, so I'm coming here in hopes that someone can!

A few days ago I noticed that one of my females was a bit slower than normal and had some issues staying up (she would sink), but I fed her a pea and she's completely fine now! I assume it was unrelated. When she was back to her normal self (during zoomies) I noticed that she had a red spot around where her egg area is, I took some pictures!

Today, that same spot is a bit darker, so I'm not sure if she hurt herself, or a breeding process failed (my other female is pregnant and the males can be a bit too "over-excited"). There are no other red spots on her and no signs of disease, she's schooling with the others and she's still eating, getting the zoomies, and exploring. My other fish are also completely fine!

My tank parameters are all good, (0 Ammonia, 0 Nitrite, 20-30ppm Nitrate) and has remained the same for over a year now. Their tank is a bit small for them, because I made the terrible decision of listening to the fish store instead of asking on forums about things (they told me a ten gallon tank is fine for four corys). I have a 20 gallon long cycling for them right now, though! I just wanted to explain that so I don't have to go back to it in comments.

I tried getting the pictures to be as clear as possible but she's a very hyperactive fish so it's hard to get a good picture. The first two are from a few days ago when I first noticed it, and the last two are from today, where it has darkened. I really hope I can get some help here because nobody on Reddit replied.