[my 2 yorkies]

hi everyone, i am new on here and i really need your help.
i have a 1 1/2 yr old yorkie and about 1 month ago, i noticed him urinating and there was a puddle ,but then he started to walk around and try to urinate about 15 to 20 seconds and nothing came out. so i took him to the vet and i brought in a urine sample which i collected myself. the results of this test was very small amount of blood and no crystals, so they put him on clovamox for 10 days, which he might have gotten slightly better , but then went back to straining.
then i took him back with another sample and it came back with no blood and a few struvite crystals and concentrated urine. so he put him on zenaquin, which he got really really sick from that drug. he was a total space cadet and could hardly move and throwing up. so they recommended a sonogram, which i did 425.00 later and then he said he needed to do a catherer to get sterile urine.
all in all he has no stones, they have no idea what is wrong.
now the vet said to switch his diet to royal canin urinary so canned food.
he has been on a raw diet for a year , and i think royal canin so food is no good, it has nothing good in it, a lot of by products.
is there a similar canned food that i can feed my baby? or can i cook for him. i look forward for someones help.