Letrozole can change hormone levels over time, and this can indirectly slightly weaken the pelvic floor muscles, but not usually to a severe degree.
Firstly, I would ask your GP surgery to test a urine sample for you, to check whether you have a urine infection that can cause these symptoms.
You said that you have had recent surgery in the pelvic area. Do seek advice from your hospital team about this. They may suggest that you also try doing some pelvic floor muscle exercises. You shouldn't be experiencing severe urgency, so do let your GP know about this as well.
There is information about pelvic floor exercises here,
