I know you're disappointed, but that's a HUGE chunk of time to take off. I remember when I was trying to run sub-20 in the 5K. I was sure that I was close for about a year and had a long string of 20:12 finishes. Then finally, it happened and broke through with a 19;48. I will tell you that as you get faster, you cease losing chunks of your times. You're getting closer to the sharp edge of the razor. At this point, assuming all things are equal with your training, while you should have no doubts that you'll get there, just know that it may take a while, you will have to find another level of "digging deep", and the right course on the right day. But it will happen. Keep plugging over the summer and one a cool day in the Fall, it'll happen.