On the day you ran 16:37 I guarantee you could have run under 5.
But, you haven't done any workouts for 6 weeks...so what did you expect?
Obviously, there are people who can run sub 5 on no training at all. But, compare yourself to yourself.
Also, to maximise your potential in the mile you need to do some very specific workouts that you haven't done. 10k pace workouts won't cut it. Strides help footspeed but don't develop mid distance specific endurance. You need to do workouts such as 3 FAST 600s where you are gasping for air with full recoveries between. You can get more complicated but just that simple addition to your workouts once a week, I believe would get you under 5.
What's your fastest 400m time?