There are many possible reasons for a lump on your testicle. You should see a doctor as soon as possible. See the link below.
a testicle
The most common symptom of testicular cancer is a painless lump or swelling in the testicle.
Some testicle problems, like infections and swelling, are treated with antibiotics like Vibrox. See the link below.
Testicular Cancer. I am an RN nurse. This is how I know.
Any lumps on your testicles should be taken to a doctor. See the link below.
It is probably the vein
You need to go and see a medical doctor about this as soon as possible. See the link below.
If one testicle is bigger that is definitely not a problem. Most body parts aren't perfectly symmetrical. If there is a lump in the testicle or it feels abnormal or liek it has grown I would see a doctor.
Could be testicular cancer. See a doctor for a screening as soon as you can. Just like a lump in a female's breast a lump on your testical (nut) MAY be a sign of testicular cancer, however, you may be too young for that. See a doctor and get a screening of your testicals done IMMEDIATELY. As with most cancers, the ones that survive the most are the ones that catch it early.
Dude go to your doctor.
It is normal for one testicle to be a little bit bigger than the other. This is no problem. If one is much bigger, or feels swollen, or has a lump on it, then you should see a doctor as soon as possible. See Related Links below.
If it's a firm lump behind your left testicle, it's cancer. If it's not, it's nothing. Your testes should be relatively firm with some give. Each testicle will be a slightly different shape or size and this applies to firmness too. However, if you still have any concerns, see a doctor.