this condition is called hematospermia
Hematospermia is almost always a benign condition. There are multiple causes for hematospermia.
They include benign and malignant disorders of the prostate gland, seminal vesicles, spermatic cord, and ejaculatory duct system; urogenital infections including sexually transmitted infections (eg, chlamydia, herpes simplex virus, gonorrhea, trichomonas); metastatic cancers; vascular malformations; congenital and drug-induced bleeding disorders; and even frequent daily ejaculation over a period of several weeks
initial evaluation is with history, physical and urinalysis.
cbc, and coagulation profile like pt , ptt , is also recommended.
ultrasound of kidneys and bladder also helps in ruling out source of blood from these organs.
i would recommend seeing your doctor and getting above tests. and as you had bowel cancer , your doctor needs to rule out metastatic disease also.
In most cases, the evaluation will not identify a clear cause of hematospermia. Thus, there is no specific medical or surgical treatment for the majority of patients, and the condition will usually resolve spontaneously.
most important treatment is reassurance.