hi b0b.
The veiny things you are feeling could be where your vas deferens (the tubes that connect your testicles to your prostate and urethra) attach to your testicles. These are completely normal, and should be felt on the back side of your testicles. If you feel them in other areas, you should get this checked out! I remember feeling discomfort while I was your age for awhile, especially while I was going through growth spurts. Have you been growing quickly lately?
I think that if you trust your parents, you should talk to them about it. If you have someone like a counsellor to talk to at school as well, they can guide you in the right direction!
Remember, doctors are there to help you, not to make fun of you or laugh at you or get mad at you!!