I have been consipated for two days. i finally used the bathroom but noticed bright red blood when wiping during the bowel movement. i strained during the bowel movement. i never had this happen before. can straining cause it? do i need call doc?

Likely related: To constipation that should be avoided at all cost going forward. Always a good idea to let you doc know as a simple exam may reveal the diagnosis most of the time.

Very common: This is very common with constipation and straining. If it was a hard, large bowel movement then there is a strong likelihood of anal fissure that will heal on its own completely. If it continues, you’ll want to see your doctor but in the meantime increase your water intake, fiber intake, and take a stool softener like Miralax.

Rectal bleeding: probably not cancer at age 37 - sounds like constipation - but you need a diagnosis, most likely hemorrhoids, which can only be diagnosed in person with rectal exam and probably anoscopy (small clear plastic tube that goes about 1-2 inches up through anus to visualize and diagnosis hemorrhoids)