something is always wrong with Rex!!

Ever since I got Rex their he always seems to get sick and have to go see the vet. My females never have to go to the vet. The other day I was petting Rex and I was getting ready to give him a bath and brush him, I saw this big lump on the side of his belly.  when I touched it, it felt really squishy and seemed like their was a lot of fluid in it. After I saw that I jumped on my laptop and searched up what it could be and the first thing that pops up is it could be cancer, so of course I got all freaked out and called my mom. She told me to wait till Tuesday and take her after school well thats today and I took him and they are all booked for today and tomorrow. They said they would call me when they are free, I really don't like this vet because they are not the nicest people. I just hope it doesn't get any bigger then it all ready is. I think it is just a really big cyst or it could even be an infection, I have been keeping in side the house so he is not running up and down with the other two. I don't want it to pop and then have an even bigger problem on my hands. I just hope he can get in to the vet soon and be healthy again !