Please, please be very careful about this!
Your curvy posture that you describe sounds like you have slight lordosis (a front-to-back curve) in your spine. A slight curve shouldn't cause problems but you do need to be careful with it.
I have very bad back problems and help run a website for people with spinal curvatures. I've seen all sorts of doctors and pain experts, so I know that it's vitally important to keep stretching and moving rather than sitting or standing in one position for too long.
Whether you're sitting at a computer, or practising your violin, make sure that you move every now and then - shrug your shoulders, stretch your arms out, swing your arms and give yourself a shake. Bending down to touch your toes will be especially good for you as it will stretch your lumbar (lower) spine. If you keep moving it will prevent your muscles from tightening up, which can ache and pinch nerves which cause the sharp pains you describe.
I have a lot of trouble with my shoulder muscles and playing the violin/viola makes it a lot worse. I have to have steroid injections every few months to relax them, as they go into spasm and won't relax. I had the injections a few weeks ago and I am doing all I can to prevent the muscles from seizing up too quickly - and I can tell you that moving and stretching really helps! Also, there's a Chinese remedy called Wood Lok oil, which is about 100 times stronger than Deep Heat and feels amazing on your muscles. It tingles for hours after you put it on and really helps your muscles to stay relaxed. It smells veery strong but it's worth it! You can get it on Ebay or from Chinese medicine places, and it's well worth trying.
Swimming will be good for your back; as you get older you might find that you get more lower back pain than most people do. This is because of the exaggerated forces on your spine. If you build up your core stability muscles now, it will really help you in the future

Hope this helps - good luck! It saddens me when I see talented musicians have problems with pain as I know how difficult it gets to play.