Doctors prescribe a lot of treatments with very poor statistical outcomes; braces are one of them. If you have a fundamental incurable problem that requires a brace to ride a roadbike, get a different type of bike.

For now:

- Make sure you have the right frame size

- Put a MUCH shorter higher stem on that bike - and if that doesn't work, stay off it until your is stronger

- Do core exercises. I'd consider kettlebells if you can find a coach or have the experience to learn safely from a book (which as a 19 year old with core problems you probably don't.) Do NOT do sit-ups: they're now considered an unsafe exercise even for people without health problems - as well as ineffective for the muscles people think they work. (People think they're an ab exercise, but they mostly work the hip flexors, which won't help you at all.) Consider Pilates and look at

http://www.mayoclinic.com/health/core-strength/SM00047

http://www.menshealth.com/fitness/core-workout-4

Re situps - and even crunches:

- They target the contractive core muscles, which aren't the ones you need to target

- Sit-ups target the hip flexors, which attach to your vertebrae in a scary way that can create misalignment of the vertebrae and intense wear spots on the lubricating discs between them. You do NOT want this!

- The repeated movements are bad for the vertebrae:

http://www.newsweek.com/blogs/the-hu...on-t-work.html

Most of all, gather knowledge first and exercise second. Read articles from good sources, then order the books referred to. Ideas about core strength have changed a lot in the past few years and we now know that a lot of the old advice was harmful. The ultimate book (literally) is probably this:

http://www.amazon.com/Ultimate-Fitne.../dp/0973501804

..Which is probably cheaper to order from the authors website:

http://www.backfitpro.com/