Hello and welcome to HCM.
Thank you for writing to us.
Firstly, the gastrointestinal tract and the urinary tract
are two different systems all together. Yes, the irritation caused during IBS
can result in inflammation of the gut and put some pressure on the bladder, making you feel like you need to urinate, but this will not be that severe.
Next, if you are experiencing the itching, this is an infection for sure. If the Trimethoprim
is not helping, please visit your doctor. The possible cause could be that you are resistant to trimethoprim, in such a scenario a different antibiotic will have to be prescribed to you.
The itching is most probably due to the itching, but an allergic reaction
the trimethoprim can also cause itching/rash
like reaction, but I doubt this could be the reason due to the location of the itching.
I hope this information helps. Do write back to me for any further information.