Thank you for your question, it’s always a good idea to ask questions when you notice changes in your body or things you find concerning!
It is not unusual for most young men to have one testicle that is slightly larger than the other; however, if you notice a major difference in size, especially if it’s a change from before, you should see your health care provider right away. Changes in apparent size of your testicle and one-sided stomach pain can be caused by a hernia, where part of your intestine pushes its way through a small hole in the abdominal wall into the scrotum (sometimes from heavy weight-lifting) or it could indicate a problem with your blood flow involving the veins of your scrotum. But it is very difficult to know the specific cause (without a thorough evaluation), which is why it’s important that you see a medical provider. Tell them about the pain, the location, when you first noticed it, how it feels, how often you have it, what makes it worse and what helps to relieve it. It’s also important to tell your provider if you are sexually active. Your provider will likely examine you and ask additional questions to ensure the right diagnosis is made to recommend the appropriate treatment and help you to start feeling better!