my cat has been sick for over 3 wks. help

Question
my male cat,nutered and up to date on all shots.12 yrs.old started with a small lump on his back,next to the spine,rear part of his back and fever.the vet thought it was absesed, put a needle in,but nothing came out.gave him a shot and bottle of antibotic,he began to get better,then when med. was gone, he got same systoms again(sleeping alot can hardly walk,fever,not eating much. (it seems to be all in his rear body,and back legs.) got new antibotic, and blood test. test indicates infection, antibotic not helping, vet switched back to original antibotic,he's not getting any better. vet talked to 2 other vets, they are all stumped and recomend xrays on monday. the lump went away after first vet visit.help please

Answer
Hi Debra!  I would definitely do the x-rays on Monday as this may give the veterinarian a better idea of what is going on and why your cat isn't getting any better.  Has the antibiotic Baytril been prescribed?  Baytril is a very strong antibiotic and is known to knock out a stubborn infection.  
Is he urinating okay?  Male cats tend to get urinary crystals which can cause a urinary blockage.  This can cause the cat to become very ill and a urinary catheter will help to drain the crystals.  If he is urinating okay, and has been on Baytril as well, I'm just as stumped as they are.
Doing the x-ray truly may help decifer what is going on with him. I wish I could be of more help.
Please keep me posted and let me know how he's doing.
Hilary