The symptoms of feline lower urinary tract disease (FLUTD): frequency, straining, blood in urine occur in male and female cats, and are usually unassociated with "infection" but rather inflammation. Culture of the urine of these cats rarely reveals bacteria, therefore there is no infection. The terminology is important to understand that while an antibiotic may have been given to prevent infection as a secondary result of inflammation it is not a primary treatment for inflammation. There are veterinarians who routinely use antibiotics in these cases, however, I no longer do.
To answer your question, FLUTD once it occurs is a chronic condition, managed not cured. Any diagnostic tests your doctor wants to do now are selected to help choose effective long term management, perhaps saving your cat future episodes and saving you money in the long run. Its what your doctor and you dont know that makes the future problem.
Also nothing you did with soaps or litter boxes has anything to do with the disease diagnostically or therapeutically. Its a disease of inflammation of the lower urianry tract, sometimes associated with crystalline material or other debris that in male cats at least can also cause obstruction.
I suggest you let your doctor pursue whatever avenues he/she feels necessary for best long term management.
Arnold L. Goldman DVM, MS