I've Been To The Drs Today And Been Told I

I've been to the Drs today and been told I have a urine infection ,been prescribed Trimethoprim, my stomach is very painful and now just vomited half a pint of brown liquid. I've not eaten for 2 days but did drink a small tumbler of cranberry juice, is this normal, is it the cranberry juice or a side effect of Trimethoprim