Like others mentioned, other kidney problems are good ideas for your problem. Also sometimes doctors miss yeast infections because some types of yeast are resistant to being cultured outside the body. Antibiotics generally make yeast worse, so maybe you should try antifungals (from your doctor). ON your own, you also might try unsweetened cranberry juice. It's pretty good for yeast (and somewhat good for many other microbes).
But go visit an urologist because it's possible that this sand it is blocking a part of your urination system, in which case he'll give you something to help the crystals go away..I have been uffering for like 3 months now and I know how frustrating this could be.But then again if this is your cause, do not worry ...it's easy to fix.Good luck!
Hey!Myabe it is crystals in urine..I mean sometines "sand" passes to the urination system from the kidneys and it feels like you say.I kind of have the same problem.All my exams are fine but I have the urge to urinate frequently, my back hurts, I feel something weird in the abdominal, as if it's full or something like that.Actually this happens mostly right after summer, because the kidneys work overitme during Autumn. I had to take sooo many urine tests before they tracked some crystals in urine.You have to drink lots of water and do some jogging, juping..anything that would move the crystals aout of your bladder. You should go for an ultrasound of the kidneys/ bladder to eliminate other causes.But it seems to me we suffer from the same thing!