Those are some great times for a sophomore. You're on the right path, I would just make a few minor adjustments. Take your easy days easy, and your hard days REALLY hard.
I was right around your times as well around the same time, and what really boosted my time was in-season, I shifted to doing 4 "hard" workouts each week. Meaning, 2 tempos and 2 intervals. Make sure you get some more variety in your interval workouts. I did 400ms, 600ms and 800ms mostly. Sometimes ladders of 400-800-1200 and back down. Sometimes we went to a hill that was about 600m long and just did our intervals on that to build strength.
My mileage was pretty low, maybe around 40mpw in season. My easy days were very easy. Running without a watch for 5-8 miles, and another mile for a warmup/cooldown. Always took a Sunday off. I did a lot of two-a-days to keep my mileage up, and I never wore a watch for those either.
Off-season I probably ran mostly at 7:30 pace for all my running, throwing in fartleks and intervals. I got up to 80mpw but that was mainly for XC season. In the winter, I ran indoor track and was down to probably 50mpw.
One thing that really helped me was teaming up with the other stars at high schools in the region. We would meet up once or twice a week and train together. We all ended up running at D1 programs.
The above is only meant to be an illustration of how varying your training and the stimulus you give your body can help you break that plateau. You're on the cusp of being either a D3 runner or a D1 runner at a serious school. You have so much to gain, so keep it up and don't get yourself down.