Don't know how much you can accomplish in 3 weeks. It takes about 4-6 weeks to get benefits from speed work. You may want to not drink as much so you will not have the swishy feeling in your stomach. For a sprint, you shouldn't need that much to drink. But the only real way to get faster is to include some faster paced running in your training. Once a week, you will have to do either speedwork, like Christri25 suggested or some tempo running. Tempo would be the pace you could sustain for about one hour. Its usually a little slower than your 10K pace. A weekly tempo run of about 20 minutes can do the trick. Make sure you run a least a mile to warm up and a mile to cool down after these efforts.

A lot of triathletes will focus on their stride rate when racing. Take shorter but quicker strides. Think quick turnover. A good gauge is you need to have 21 strides per every 15 seconds, 22-23 is even better. I notice a lot of folks that are not strong runners overstride. You would be surprised how much faster you will go. Another thing to remember about sprints is that they are sprints. The last mile of the run, if you are racing, has got to be all out. I mean, heart pumping, touge hanging out and the I am about to die effort. The bad news its hard, the good news is the race is short and a few minutes after you cross the finish line you will be fine.

Good luck.

Never had a stitch while running? I think all of us had. Usually it is hyrdation caused. Too much, too little: I've cramped some because of both. My remedy: breather deeper and run faster. It will go away.. or just be overtaken by the burning in your legs :)

As far as speed increases... blueriader was right, it DOES usually take about 6 weeks to see the results of speed work. BUT get started now and you'll def. feel some benefit. I don't like to use HR as a guage of running effort, but I've been running for 1/2 my life, so I know my exertion levels well. To start, I'd run some 1/4s and 1/2s and work your way up. Run them at your desired race pace ( end of season goal pace) with 2-3 minutes rest. Start with something like .25/.50/.50/.25 and build from there. The goal is to get to mile repeats.

Improvements in fitness won't come quickly. To make significant gains in that short a time, I suggest the following:
1. Improve technique - almost every runner overstrides to some degree. You might improve economy 1 or 2% in a couple of weeks, but you could never improve fitness that much that quickly. See the Evolution Running DVD or Triathlete's Guide to Run Training book at EvolutionRunning.com

2. Rider at high cadence. Research shows that even for riders who can go fast grinding a big gear, every triathlete runs faster after spinning.

3. Fuel and hydrate well on the bike ... 20 oz water + 300 calories of carbohydrate per 150 pouds per hour.

4. Phosphate loading ... gatting enough sodium phosphate allows your blood to carry about 1% more oxygen. There is good science behind this. Try Race Day Boost E-Caps.net

Good luck, Ken Fitness-Concepts.com