Is it normal that my sweat sometimes smell like pee?

The yellow pit stains are caused by the ingredients in antiperspirants. Switch to deodorant and you'll be fine as far as that goes. Deodorant will also help with the smell, since antiperspirants attempt to make you not sweat, but it still smells like piss, deodorant makes it so what you do sweat smells delicious.

Sometimes when I sweat it smells like nasty garbage and I feel like the toxic avenger. You post a lot. You just posted about having a hairy naval right? That is cute.

it isn't normal, but is often temporary

I can only think of 3 reasons. lack of water, improper diet, and the third one you needn't worry about at first

drink more water, eat a balanced diet -- if the problem still persists, consult a doc

deoderant

Sounds to me that your body is having a hard time at filtering out toxins. (Could be an problem with your kidneys) Try drinking more water and see a doctor.

Pure cotton is good to wear, as bacteria like it less than synthetic fibres.

You sweat out toxins, you piss out toxins.

Sweat and piss aren't overly seperate things.