ok so my dog is one and a half years old its a chihuahua
i just changed it's food to Canidea (before it was iams)
ive notice that he couldn't jump on my small bed anymore, but befor he was able to jump on my mom's kings size bed
also i noticed ever time he gets up his bone will have this little cracking sound and he would whimper
but when he jumps down my bed it seems he have no problem
he doesn't walk/run that much anymore, but he still can walk up the stairs
compare to my other chihuahua he shivers a lot
he rarely eats on his own but when i feed him (mixed the food with water so its soft) he would eat about half a cup to a cup each day
he doesn't have a lot of fat on him (i can see his bone), but on my other chihuahua she has some fat but i still can see her bone
can he have arthritis even though he is so young and never had a injury,but he has a lot of the signs for arthritis

ok so whats wrong with him
and I KNOW i have to get him to the vet and I will tomorrow (today is sunday)

but i just want to have an idea whats wrong with him
and if i take him to the vet will he be ok or die?
and i know when i bring a dog to a vet it will never be cheap, but how much do you think it would be?

and please don't say im a irresponsible dog owner because i am and i love my dogs it's just i just noticed this. so PLEASE help!