Hope this will help you.
Since you have done army, I would assume that you would have
passed the 2.4 in your younger years.
One of the things that you might want to consider is that your
body needs to be conditioned to be able to take the strain for the
2.4km run. So if you do not have a regular exercise routine, you
might want to start with shorter distances & make sure you know
your limits.
Jogging will not give you the time needed to pass the 2.4
run.
You need to develop a wider stride that you are comfortable
with, but still at a relaxing pace. When you look at how good long
distance runners do it, they look as if they are brisk walking, and
they have very wide strides with their legs slightly above the
ground and their breathing is very slow & consistent. Relax you
hands and use them to give you momentum forward.
So you would need to breathe in through your nose and out
through your mouth. And if you find that you are breathing in &
out from your mouth, it means that you can't go very much
further.
Lastly, when you feel you can't go any further, make sure you
open up your stride and sprint the last 50 to 100m, and do not stop
but continue walking when you reach your finish line until your
heart beat slows down. ( Please don't do this if you have not been
exercising regularly and eating well !!! ) - this sprint will
definitely improve your timing in the next run because you are
breaking the limit that your body can take. Make sure you stretch
well before and after runs. Set targets for yourself, may be run 2
rounds and sprint 100 m and then progress to run 3 rounds and
sprint , then 4 rounds and sprint....
You will find that it may seem harder to have bigger strides
initially & may take you some time to feel comfortable with the
bigger strides but this change will give you better breathing to
cover longer distance & better timing too.
This is the same concept with swimmimg free style, you need to
stretch your hands & reach further forward to strengthen the
muscles of your arms to be a good long distance free style swimmer.
And because you are reaching forward, it gives you more time to
take slower & deeper breaths, but if you have small strokes,
you would need to breath faster and will run out of breath after 1
to 2 lapse.
May be you can consider swimming or cyclying to improve your
breathing, becasue running can have a higher risk to injury to our
legs as we get older.
Lastly, when you are running, just think of something else when
the pain comes, like an encouraging phrase, as for me I would
repeat this in my mind constantly" I can do all things through
Christ that strengthens me"...
Not sure if this will help you. I am not a professional trainer,
this is just my personal method.
All the best, and hope you pass your 2.4 soon.