8 month old Pomeranian yelping for a month, for the past few days woobly

My Pomeranian is 8 months old and a month ago he started yelping in his sleep. We’ve then noticed that it’s not going away and he started randomly yelping in the middle of the day out of nowhere. We took him to vet, they couldn’t find anything. As the days went on, he started doing it more and more frequently + started putting his tail down. Still vets don’t know what’s wrong but said that his right patella is luxated, gave him pain meds but he still continued to yelp. He ate and drank normally, sometimes even was happy and ran etc. but the yelping continued. A few days go by, I notice that he has fleas! Asked vet, he told me to give him Advantix <= 4kg (he has 1,2kg). We do the treatment and the next day he’s still yelping and starts woobling… very unstable when he walks. 2 days go by, the walking/standing gets worse, we take him to the vet again. Vet (new one) says he has both luxating patellas but that it’s not the reason why he’s yelping, but still doesn’t know what is. Gives him again pain meds, he still yelps for the whole day and night, while not being able to stand/walk. I read online that the flea treatment can cause issues with neurological system (like not being stable etc.) and that the treatment isn’t supposed to be given to puppies under 1,5kg. We take him to the vet again, they still don’t know what’s wrong (all the bloodwork is ok). They don’t know if yelping is tied to this not being to walk/stand or was this caused by the flea treatment. We went to the vet again today, they have this (idk if it's x ray or what) and we need to wait for them to check before getting back to us with the diagnosis. He can move better than yesterday, can walk and stand on his own but he's still woobly and yelping.

Hello - Im so sorry to hear that this is going on for yourselves and your dog; it sounds distressing.  On these pictures, the patient is lying in a very tucked up posture and the radiograph is quite hard to read; your vet should have been able to read this better than I can, looking at both the radiograph and the patient in real life.  I imagine that they will have examined the abdomen, spine and legs to see if they can better locate the source of any pain, and also carried out a neurological examination.  This is a systematic collection of tests designed to test the function of the brain, spinal and cranial nerves.  It can take some time to do, especially if neurology doesnt happen to be their speciality.  Having done all of this, on most occasions a vet will begin to suspect which body system they are concerned about and from here may conduct further tests or reccommend a specialist.  Sometimes it can be difficult to tell eg muscular problems from spinal ones.  I have my fingers and toes crossed for yourself and the patient; plesse will you let us know how things go from here?