Some people run with tense shoulders, so its possible that its running related. On your next run, try forcing your elbows lower. Also make sure your hands move in parallel to your body rather than across your chest (so you're not twisting your shoulders).
For your breathing, are you warming up for the first ten minutes or are you getting straight into the run? Try either running slower (e.g. at least one min per mile slower) or walking for the first five minutes and then gradually pick up the pace for the next five mins so you only hit target pace after ten mins. This gives your body a chance to adapt to the extra demands of running rather than a sudden change.
If these tips don't help, as RicSure said, it would be best to get a proper diagnosis by a doctor.
The other simple thing to do is to take a rest week, either by cutting out one or two sessions or by halving your weekly mileage and seeing how you feel the week after. You should feel better on the return week (even if you haven't been overtraining) but if you see a dramatic improvement then this would be an indicator that you are trying to do too much, too soon.
There's a couple of good reasons why a beginners plan has a maximum of 10 miles:
- Your long runs should be significantly slower than your HM race pace, so the time taken to cover the ten miles should be roughly equal to your race time (i.e. think time on your feet rather than distance).
- The long run is necessary to build endurance, which means you will be tired and your running form will deteriorate in the last few miles as you push past your current endurance limits. This increases your risk of injury. The ten miles is a compromise of going long enough to build endurance whilst minimising your time in the injury "danger zone".
Just as important for your first half, if you go more than 13 miles in training it will take some of the shine off completing the distance in your first HM. It will be a special feeling when you complete the distance for the first time.
If your race is on Sunday, then this week should be "taper" time with limited mileage so you are fully rested for the weekend. You should only run roughly 50% of the weekly distance you have been doing in training (if I mis-read and the race is on the 12th, then about 75% of weekly distance this week, and 50% next week). Your last pre-race run would be either Friday or Saturday, and should only be 3 or 4 miles at most. Personally I prefer to get out on the day before the race for a short run to loosen up and reduce pre-race nerves, others prefer to have a day of complete rest prior to the race.
Very difficult to help from the info you've provided.
As some pointers of potential things to look at:
- If you run too hard then you won't be able to breath in enough oxygen to meet the demands of your muscles which leads to a breathless feeling. Simplistically, this is your body saying you are running too fast, so you need to run slower. Have a look into V02 max and things like interval training to improve this.
- There is exercise induced asthma that can affect people under hard exertion, so it would be worth consulting with your GP to see if this is possible.
- It could be anxiety under race conditions (i.e. the athletic equivalent of "stage fright"). Not really something I'm familiar with, but maybe take part in races more frequently (e.g. weekly park runs) to reduce the anxiety through familiarity?
- there is a large mental aspect to running. After having a bad race where I had to walk for a while, I found I had a mental block where I had a strong desire to walk for a little bit for the next couple of races. It took a few races to get over this, and many hard training sessions where I forced myself to cover the distance and not quit.
Don't underestimate the effect of the heat, which would have shown in the last few miles.
You think the long runs were too fast and had a detrimental effect, but what were the symptoms of this?
- If you went into the event feeling a bit tired (especially the legs) then stepping up to a harder training schedule wouldn't help.
- If you struggled with endurance in the race, then a more advanced programme would help build this up for your next event.
If your looking to do a spring marathon, that's roughly six months away. As the marathon plan will be 3 to 4 months, this gives you a couple of months (after resting up from your recent marathon) to build a base mileage. Depending on how this base building goes, you can decide whether to take on the extra workload of the more advanced plan.