Kickin' it up a notch

For the past year and a half, I have been a runner.  I have run at least 2 - 3 days each week, although I usually run 3 - 4 days.  I typically do 2 - 3 short runs (3 - 4.5 miles) and one long run (7 - 10 miles).  When I began running, I could barely make it through 1.5 miles, so this is quite the accomplishment for me.  I have completed numerous 5K's and two half marathons, and I'm already signed up for my third half marathon.  Through it all, my pace has remained relatively the same.  Sure, I run a bit faster than I did when I started running, but I'm not much faster than I was when I ran my first half marathon last April.  I keep justifying it by saying that I'm just a slow runner.
Recently, I have noticed myself running a little faster.  It's not something that I can maintain for miles, but when I look at my garmin, I often catch myself running 9 minute miles, and sometimes even 8.5 minute miles.  Unfortunately, seeing this pace blinking at me on my watch causes me to instantly panic and think that I'm pushing myself too hard.  After all, I don't want to puke or collapse at the end of a 3 mile run.  But, I now realize that I'm never going to get faster if I don't push myself a little.  When I first started running, I struggled through 1.5 miles.  It wasn's easy, and I thought I was going to die the whole time, but I didn't.  I now realize that I have to let myself feel that way again if I am going to build up my speed.  So, I'm going to incorporate some interval training into my weekly runs.  I'm confident that I can go faster, if I just let myself.