orthotics are a short term fix for a problem and create a long term dependency.
i was in the same spot as you. i developed a bad case of posterior tib tendonitis towards the end of my high school years. i was told i over-pronate and needed custom orthotics. i went along with that because pretty much everything i'd read (in rags like runners world) said orthotics would help with over-pronation, which was the cause of a lot of running injuries.
getting the orthotics seemed to help. i ran the first part of the seasons injury free. but once i switched to doing fast workouts and races in racing flats, i was screwed. all of a sudden my feet and legs were going through the natural motion the orthotics were preventing. i may as well have gone from ZERO miles per week to running hard track workouts. i was an injury time bomb, and i got plenty. an even worse case of posterior tib tendonitis, achilles tendonitis, patellar tendonitis, IT band problems. and running in the orthotics gave me neuromas in both feet because by "correcting" the overpronation, it put unnatural stress on the smaller toes where it didn't belong.
as long as i ALWAYS wore orthotics in my runnings, racing, and walking around shoes, i would have reduced some of those problems (neuromas excluded). but they also made my feet WEAK! walking around barefoot was painful. why would you do anything to make your feet and lower legs weak? it makes NO sense. don't get dependent on a crutch. get strong instead.