Thanks for your query,based on the facts that you have posted it appears that you have noticed a red string coming out through urethra with urine.
This is a blood clot which might have originated either from urethra or bladder.
Please consult qualified Urologist
for clinical evaluation and get following basic tests done to
come to diagnosis.
1) Routine urine test
scanning of the abdomen to rule out infection in bladder or presence of stone.
Please take broad spectrum antibiotics like Cefotaxime
along with anti inflammatory medication like Diclofenac
Ensure to drink more water.To keep your urine dilute.