Hi! My guinea pigs name is Oliver! He is my best friend! He is under a year old! I had to give him a bath two days ago because he has long hair and has knots! So I gave him a bath and cut his hair! I was brushing him today when I realized his butt is swollen!! Like it’s big! I have no idea why! I have a pic below! I have done a few things different that I can think may have caused it! He got a new bedding? Maybe the soap I used for his bath? And I had no idea guinea pigs had grease glands and so I have not cleaned his! Could one of these be a reason? Someone please help! Now that I know about the grease glands I am cleaning it! But what could be causing this! He squeals when I try and looks down there! What is wrong!! And he never lets me look at his underside so I just now seen that his under carriage is dirty! I have cleaned it after the photo! And this is the soap I used! I was going to get him special guinea pig soap but for that day to get the knots off I used this please can someone tell me what wrong!? Thank you for taking the time to read this! I appreciate it!