Try mixing up your routine.
One to two days a week add in a sprint day for your run. Run 10x 400's or 6 x 800's . Aim for a faster pace than you normally run. (for example, this is just an example you can google specific routines, if you can run a 7:15 mile pace try to run 800's at 3:14 min which equals about a 6:30/ mile pace. 400's at 1:34 min which equals about a 6:20/ mile pace) Eventually you will run faster even if you are not hitting your goal times.
Also try adding in a long run one day a week if you are currently not doing so (for example if you normally run 3 miles a day then for a long run then run 5). Long run should be a slower run no faster than a minute off your normal running pace, some even run it slower.
Try changing where you are running at. Your body can become used to the same route.
Try adding in a hill day every 5-10 days.
Remember to stretch both before and after and do some sort of warm up and cool down.
Most importantly listen to your body. Soreness can be normal. Pain is not!
Check with your schools' track or cross country coach. They might be able to make a special routine just for you based on where you are and where you want to be.
This is all great advice. I definitely agree speed work is crucial. One workout I do about once a week is as follows:
Stretching + Warm-Up
1 Mile easy
3 min Hard Running-- Here, you are breathing hard and not able to speak comfortably. You're in pain.
3 min Easy to Moderate--Here you should be recovering, but still running (This is your rest)
Repeat the 3-minute sets 3-5 times
(easy) Jog the rest of the way home.
Some notes on this workout:
This format is called a fartlek, and the main thing is to
keep running. The goal is to learn to be able to turn on the speed without taking any real breaks.
I love these runs because it's great speed work for the mile event, and it also ends up being a longish run for me (5-6 miles), so I feel like I'm checking two boxes at once.
Additionally, incorporate some bodyweight exercises (or use weights if you have them) like squats, mountain climbers, and box jumps. Try and be explosive in these motions, as it will train your muscles to activate faster and with more force.
Finally, abdomen cramps are something I've struggled with for years. For me, the biggest thing is being properly hydrated and warmed up ahead of time. Make sure to be drinking all day, all the way up to the starting line. More water (within reason) will help your body, not cause more cramps. Also, get a good warm-up in. You want to let your body know what's about to happen.