@keith4980

If you are not diabetic, nor do you have kidney disease, and all the tests have returned negative:

In your case, IMHO, the likely reason there are "bubbles" or "foaming" forming in the toilet bowl, are simply the physics of a strong 16 yo urine stream hitting the surface of the toilet water at high force and creating bubbles/foam.

Be assured, as you age, your urine stream will decrease in force, and there will be less bubbles; unless some pathological process is happening.

I have sons, 2 of them, grown now. The only reason one of my 16 yo sons would have come to me with this question would be that perhaps they'd had unprotected sex and are worrying they may have caught some disease.

Am not meaning to offend, but if you are of like mind of many 16-21yo males: time to go see the pecker checker to allay your fears.

Any burning and stinging when urinating?