I think SCIfor55 has a good point. If you are refluxing urine up your ureter due to high bladder pressures, especially when reflex voiding (which can be determined by doing a videourodynamics study), having the ureteral stent in place can actually now make it easier for colonized urine to go from your bladder to your kidney, causing a true UTI.
If your stent was placed because of a swollen or scarred ureter, then the stent will allow urine to flow either upstream or downstream more easily now. Ureteral stents are not left in place long term because of this. Generally they are removed 4-6 weeks after placement. 3 months is a long time to leave one in place. You may want to discuss this with your urologist for their rationale for this time period.
A URETHRAL stent, mentioned by gjnl above, is a completely different device, placed for a completely different reason.
Here is a diagram of a ureteral stent in place.
(KLD)