Should i follow up with my doctor for a testosterone check? if i got one testicle? or it does not matter? what does testosterone do to the body?

The testis makes one of the hormones needed for your body to go through puberty and finish growing. If you are doing so at a normal rate a doctor would not order such a test just because you had only one testis. Your growth and changes through puberty are evidence enough it works okay by itself.

Not unusual to have only one testicle. You should have a thorough exam to confirm that. Undescended testicles are not unusual and can have an effect on testosterone. Testosterone is primarily a male sex hormone that affects muscle mass, hair growth and genitalia function.