Thank you for the query.
It is not the infection you should be afraid of. Blood in stool
and constipations are very unsettling symptoms. Infection would cause symptoms like: fever, diarrhea, nausea, shivers etc. It should get healed in about couple of days.
In your case with severe constipations and blood in stool you should have colonoscopy
as soon as possible. Your symptoms may be caused by: hemorrhoids, large intestine polyps, colon cancer
Please do not neglect it and visit your doctor as soon as possible.