I think you're really just suffering from lack of focus. As a former sprinter you're doing intervals, intervals, intervals. I recommend you step back a bit and concentrate on consistency
First off pull back to TWO hard runs a week, the other 3-4 run easy. Save things for the days that count. Over a two week period do intervals, long, intervals, tempo. Also, forget everything you learned about running a 400. This is a 5000, totally different animal. Long should be 1:15-1:30. Tempo about 1:00, 15 warm up, 30 up-tempo, 15 easy.
Next, it's pretty clear you go you hard, cough up a furball, then try to hang on. Bad way to run a 5K. You go out in 6, come back in 6:15, bad pacing. So get to a track and or other well measured distance and do 1000's to 1200's (5-6 of then at a time) and CONCENTRATE on running them all very close to the same pace. If that means you have to run them slower, so be it. No lolly-gagging around between repeats either, you need to learn to hold pace so keep the rest to 2:30-3:00 on the 1000-1200's.
Practice your goal pace, so after you can pace consistently switch the tempo to 2 miles at goal pace following by 15 minutes up-tempo (same WU / CD).
Remember recovery is when you improve, so push hard on the hard days and give your body time to absorb that on the easy days. You can't push the envelope when you're tired, so keep the recovery days 30-60 minutes of easy. Real easy.
Won't happen overnight, but in 6-8 weeks you should be around 18:30.