I'm going to be a medical elitist here, so bear with me or just ignore this post.
Excessive urination, or polyuria, is not necessarily a symptom of AMS so much as a sign of your body adjusting to the altitude. You did everything right by drinking tons of water (overhydration is certainly possible, but is much harder to achieve than people think). The exact pathophysiology (mechanism) of AMS is poorly understood, but it starts with hypoxia. This is pretty basic - there's less oxygen up high, so you breathe faster. Breathing faster means you breathe off more carbon dioxide than you normally would at sea level or in Denver, where you live (and are acclimated to the altitude). This is where it starts to get complicated, which always seems to be the case when the kidneys get involved.
Your respiratory drive is based primarily off of high levels of CO2 (and less off of low levels of oxygen). As you exhale excess CO2, your respiratory rate slows again, and you are no longer getting enough oxygen. CO2 makes the blood more acidic (I won't go into this), which is a large part of what comprises your respiratory drive. Your kidneys compensate for this decrease in respiratory drive by essentially mimicking CO2 increases in your blood. In order to do this, they excrete bicarbonate, a salt, into the urine. If you all recall HS biology (hypertonic, hypotonic, isotonic), water follows salt. This means that as your kidneys buffer your body's pH, they also produce absurd amounts of urine. Diamox (acetazolamide) actually works on the kidney, making it excrete bicarbonate - one "side effect" is that you piss like crazy.
This "renal buffering" effect is diminished with adjustment, as hemoglobin molecules become more capable of releasing oxygen to tissue. In other words, this won't keep happening to you unless you're just unlucky (adjustment to altitude is almost entirely genetic).
Your headache, on the other hand, is the first step to AMS. High altitude headache (HAH) is pretty much defined as a headache at altitude - no shocker there. AMS is HAH with the addition of one or more of the following symptoms: nausea/vomiting, dizziness, fatigue, insomnia. The headache is generally throbbing, as you described, and diffuse/global (70% of patients describe it this way). Photosensitivity is common, and the headache is generally worsened by motion: pretty much just like a really bad hangover. It's not at all uncommon for this to set in after descent and fade after a couple hours.
While I'm on the subject, I might as well mention HAPE and HACE. They're rare in Colorado, and it's not really understood how they happen. One leading theory is that as the pH of your blood changes, albumin - a ubiquitous plasma protein that binds tons of stuff and carries it in the bloodstream - loses its ability to bind calcium. Calcium is released en masse, and, being an ion that does just about everything, it results in vasoconstriction (your blood vessels constrict). Simply put, this "squeezes" plasma out of the bloodstream, often through the small capillaries in the brain (HACE) or lungs (HAPE). Again, this is somewhat theoretical.
Sorry for the rant! I love this stuff and think all high altitude folks should have some idea how it works. Congrats on your first 14er, and keep climbing!