Hi, Bachana and thanks for sharing your problem with us at HCM. No man has testicles that are exactly the same size, one may be slightly smaller than the other. It could very well be that yours is a normal variation. Some men do experience pain after ejaculating or cumming, whether in one or both testicles. When you ejaculate, your muscles have to spasm hard to achieve this. Therefore, any infection or swelling in the testicles, penis,prostate or tubes carrying cum can cause this pain. Sometimes, men can suffer epididymitis (infection of the tubes that come out of the testes caused by viruses or bacteria). Urethritis (infection of the urethra) can be caused by STDs. To confirm this, a doctor will have to gently examine you before prescribing medication to help treat this infection. Some antidepressants may also cause painful ejaculation. If you are on these, you need to check with your attending doctor. Even spermicides can cause irritation and result in painful ejaculation. Considering the symptoms you described,I would not worry too much about cancer - you have not mentioned any lumps in the testes. You did not, however, mention your age. In conclusion, you need to see your regular doctor to help sort this out and get treatment. I hope my answer helps. Thank you