Oxybutynin 2.5 mgs

Hi

I was prescribed Oxybutynin 2.5mgs 1 x tds by my GP as I have presented with UTI symptoms but have a clear MSU. The symptoms disappeared for about 5 days but now are back again and I am wondering whether this is an adverse reaction to the tablets or a continuation of the same problem. I have a constant lower abdominal burning sensation, with a slow urine stream. Also I feel as if the urethral sphincter will not open to allow me to pass urine and then it reluctantly does. Any ideas what is going on? My GP is on holidays!

Thanks