Help? Could it be cancer even if tests come back "normal" and/or inconclusive

Chaos, my 7 1/2 year old male labradoodle that I have had since he was 8 weeks old. He is generally very upbeat, and playful. Out of the blue about a month and a half ago he began dramatically changing. He started laying around all day, acknowledged when we called him than lay his head back down (he was always the first out of both my dogs to run to the door when he heard his leash-this changed as well), barely eating/drinking, shaking violently as he inhaled, and his hind legs seemed to have weakened (trouble getting up and down from sitting position, and started taking him a few tries to jump into my jeep which used to be a breeze).
Right before we took him to his vet of 6 years we noticed a  lump (around the size of a golf ball) in between his shoulder blades. After his vet checked him out, we found out that he had a fever of 104 and that he had dropped 10 pounds (he was originally 128-130 lbs). She seemed worried about the lump and told me to just keep an eye on it. She was more worried about his high fever, and kept stating "the lump shouldn't be causing a fever this high". They did blood work, a tick panel, an xray on his stomach area, and a urine test and everything came back "normal", never once wanted to aspirate/do a biopsy on his lump.

Within two weeks after the vet visit, my dogs health declined rapidly. He completely stopped eating/drinking (treats and all), he was urinating close to every hour and the amount of urine was twice as much as normal, looked like he was skin and bones, his legs began to give out much more frequently, and ANOTHER LUMP had popped up this time on his ribs. This lump is very hard and seems to be on the bone.

We brought him back to the vet, where they ran more blood work, took x-rays of the lump on his rib, drew urine directly out of his bladder, and an aspiration of the lump on his back (we had to directly ask her to aspirate it for our peace of mind, other wise she would not have). Again,his cell counts and other blood work came back "normal". His the urine and aspiration came back inconclusive. She also referred us to an internal medicine veterinarian who we saw a week later, and he ran more x-rays as well as a sonogram..again there was nothing.

Now my dog is close to 89 pounds, and his legs will randomly give out on him as he is walking. Not only does he have the two lumps that I've mentioned, he now has several other lumps "pop up" in different areas and almost if not all his lymph nodes are swollen and hard feeling.. He still does not eat his food (we've tried changed his food, tried mixing chicken into it, etc), he started eating his nightly treats (pig ears) again within the last week, and he'll occasionally drink his water.

I strongly believe he has mast cell cancer because his first lump will change in size, sometimes over night.

Any advice or thoughts would be greatly appreciated!!! I don't know what to do now, we are already 2000$ into vet visits, and they cannot figure out what is wrong with him. :/

[Margot49]

I am so sorry to read what you are going and for such a long time. I checked your profile but don't see where you live.  Are you near any universities with Vet schools?  I am in Central Ca and have consulted at UC Davis before.  I can see why you suspect cancer but someone has to get to the bottom if this.
Have you contacted the breeder to see if he/she can shed some light on this?  If there is a Kabradoodle National club, try contacting them

[mmm412]

I live in Virginia, I think there is a university with a vet school around me I would have to look around. I never thought about contacting a vet school, it is definitely worth a shot! Our breeder was a terrible one, we drove to PA and was told the parents were off sight, wouldn't let us know when they "would be back"and that he would only get max 45 lbs. But that 45lbs turned into 128-130lbs(: we think he may really be a goldendoodle, but we will never know for sure. All I know for sure is that there is something serious wrong with him, just can't understand why no one has been able to figure out what's causing all this.

[mmm412]

Thank you for bring the local university w/ a vet school to my attention! I appreciate it!