Should I Be Concerned About Noticing A Blood Stain On My Underwear Near The Penis Area?

I am a male , 37 Y/O I found blood stain on my underwear near pennies area , in the evening after a normal day with little hot atmosphere during afternoon No blood in urine, no external injuries found near pennies area. I found no other abnormalities , everything is feeling normal. What could be reason. I am worried.