Blood in the semen (known as hematospermia) can be caused by a variety of diseases. They include benign and malignant disorders of the prostate gland, seminal vesicles, spermatic cord, and ejaculatory duct system; urogenital infections; metastatic cancers; and vascular disorders. Most of the time, especially in the younger population, a clear cause cannot be found and it resolves on its own. A visit to a urologist would be helpful to for further evaluation.
Regarding the lump in the testicle, an ultrasound should be considered to rule out a mass, cyst or varicocele.
Regarding the blood in the stool - it is most likely a hemorrhoid (given your young age). A visit to a physician for a possible anoscopy (a small scope to make sure it is nothing worse than a hemorrhoid) should be considered.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.