Roly, I do not know about all types of orthotics and about your special case. As far as I know, however, orthotics will not correct problems. Orthotics provide some support to the foot that too weak foot muscles fail to provide. This will avoid the injury resulting from the lack of support, but it will give absolutely no incentive to your foot muscles to become stronger (which would fix the problem). So, without any additional measures, chances are good that you will have to wear them forever. There are things, however, that you can do to strengthen your foot muscles. Among them is running barefoot.
In Germany, some people are worrying that orthotics are handed out far too easily. They cure the symptom (so patient is feeling better), they are easy to prescribe and they give a constant surce of income since the patient has to come back to get them renewed [In Germany, medical insurance will at least partially reimburse you if the orthotics are prescribed by a doctor). Last year, I attended a seminar of a orthopedist who also has written a good book about running (in the language of Goethe) and he had a lot to say about this subject.
That said, the last thing I want to do is to scare you away from your orthotics. There certainly is a place for them. Currently, I am wearing my orthotics on all of my runs. I am not sure, whether they are of any help to avoid my injury, or whether they are even a part of the problem (which is possible too), but for me this is not the time to fool around with this. Once I have established that I can run regularly run long distances without getting innjured, I will look into this matter again.