What should I do about this pain?!

Measuring the volume of one pee is going to tell you or your doctor nothing useful, only the volume your bladder can hold before you need to pee! :D

Three possibilities spring to mind...

1: A urinary tract infection...nothing to worry about, your doc will sort it.

2: Holding in your pee, coupled with the nervous tension etc has strained the muscles that normally hold back your pee. There are two of them, when the upper one relaxes the pee moves down to the lower one, it is then that you will 'feel' that you need to pee. If the upper one is weakened then you will feel like you need to pee more often, even though the volume will be much smaller, simply because the upper one is not holding the pressure in your bladder.

3: You are pregnant, the changes in your uterus push on your bladder and increase the pressure on the urinary sphincter...see above...

All in all, unless your pee is coming out bright orange and on fire then I wouldn't fret it too much, have a word with your doc and don't be embarassed about it, it's all natural functions after all.
Before you go to the docs you might want to make a note of what color it is generally, dark yellow indicates dehydration, light yellow normal hydration, white/clear overhydration, cloudy could indicate infection, pink could be a small amount of blood in your urine.

I will stress that NONE of these are clear cut indicators of anything and odd wee related happenings are quite common in late teens. Honestly it happens alot, at all ages, every girlfriend i ever had always had some sort of wee related story/experience, the human bladder is an odd thing :)

All the best and try not to worry about it too much, it'll only make you nervous and we know ehere that leads ;)

Stu.

Experiences of myself, girlfriends etc and a good knowledge of anatomy.