I need Help with a undiagnosable skin condition

Hi I’m Chrissie I hope you are all well. I’m putting up this question because my vets seem unable to fathom out what is wrong with my emotional support rat Pickle he had surgery on the 28th April to remove a huge lump on his throat that came up over just four days the removal went well and he is nearly all healed up but the day after his surgery I felt a hard flat disc like thing on just below his right side ( the opposite side to the surgery) upon looking I discovered it was a very big scab which is slightly concave I checked all over his body and couldn’t find anything else on him I contacted the vet (via zoom)and he said he thought it looked like some sort of sore and as we were due to see him the following afternoon he said to keep an eye on him and he would check it out when we went. Unfortunately the very next morning I found another one on the same side just above his hip but this one was half scab and half was what looked liked a strange bluey green swelling (I will attach some photos)? We went to the vets that afternoon but our vets seem stumped as to what is causing it as some of it doesn’t conform with sores ie exact placement isn’t quite right but he did decide to extend the antibiotics (baytril) and told us to keep an eye on it he also said that it will probably get a bit worse looking before getting better as the second one was only starting to scab up and we are due to see him on the 9th May but with the vet being unsure I thought I would reach out to see if anyone has any idea what it could be and if they do to please let me know asap 🙏🏻. I did wonder if he was allergic to either metacam or the baytril he was put on after the surgery but the vet didn’t think that was it. I did bath him the day before surgery with vetericyn foam care medicated shampoo (advised by vet) which again the vet doesn’t seem to think it is the cause. None of my four other boys have any just him. He is eating well and acting as normal as a rat can be after having a 100g growth removed from his neck/throat. I caught him licking them a couple of times but it’s not aggressive licking. He is 2 years and 7 months old he has never been ill or injured before but he does unfortunately have a lot of excess skin which our vet said it is most likely a genetic thing as both of his Brother’s were the same whereas the other four rat’s I have do not have a lot of excess skin but l got them from a different breeder. I hope you have a great day🍀. Best Wishes & Stay Safe Chrissie 😊x