Im 13 and i only have one testicle in my sac i can feel the other below my abdomen what should i do?

is it cold?

it proabably retracted cuz its cold?

are you through puberty?

m1132 - my answer to that's on the discussion page!
Most boys testicles descend into their scrotum early on in their childhood but occasionally it takes until puberty. Testes need to be at a slightly lower temperature than the rest of their body in order to produce healthy sperm, which is why they are normally located in the scrotum. If you are worried the best advice I could give to you would be to go an talk to a doctor. Do not be embarrassed, doctors are used to examining every part of a patient's body. Honestly, it is better to be a bit embarrassed about having your scrotum examined but have the situation sorted out than to continue worrying about it and possibly causing damage to that teste through inaction.