I have sponge kidney and i have a fever and my baxk & stomach are killing me its hard to breathe what should i do?

Medullary sponge kid: medullary sponge kidney predisposes to stasis of urine , urinary tract infection and kidney stones. So check your self for infection first, then if no improvement or if your pain is severe you need to have a renal ultrasound, and if negative and pain is severe you might need a CT scan. I highly recommend you to drink at least 4 liters of water troughout the day as a start

UTI, pyelonephritis : It's highly possible that you have UTI. You need to have a urine test and culture first and start antibiotics right after. See your doc or go to ER. Drink liquid like cranberry juice meanwhile.