there are many causes for a painful testicle. One of the most severe causes would be testicular torsion, which sounds unlikely your case because the testicle would have sudden severe pain with a possible elevation. Other very common causes include epididymitis, which are most likely caused by gonorrhea a sexually active males. if it feels like a bag of worms, it might be varicocele, but this is usually not painful. other causes maybe injuries etc. I suggest you visit your doctor and have it checked out. Just to be on the safe side. from your description it sounded more like Epididymitis, however is not easily confirmed without a physical examination and some urine test. If it is this diagnosis, your doctor will most likely give you some antibiotics, which should relieve your symptoms.