I have braces and on random days they feel sore for no reason. what could be the reason why?

Many reasons: Orthodontics is really applied physics on a small scale acting on many bodies (teeth). As a wire works its magic of lining up teeth, it may take time for forces to express themselves along the line, and i suppose what you are feeling is different teeth starting to move in different ways over time. In the end it should not be painful after the first week. Real pain, then call and ask.

Tooth Movement: As your teeth move and realign your bite will change. You then may have random discomfort. Also if you grind or clench your teeth as they are moving you might generate the soreness also.

Adenazine di phospha: That's the chemical that makes you sure. It's an indicator that teeth are moving. Take ibuprofen, rinse with salt water, eat a soft diet, and be happy that you are makings progress.

Movement: Teeth are being moved. Like excersize, sometimes you can be sore. You should discuss the issue with your orthodontist however.

Common: As teeth move, your bite changes in subtle ways and you may have harder contact on specific teeth causing them to be sore. Often this changes to different teeth at different times. Remember, the process of moving teeth along the orthodontic wires is not a continual, smooth process, but rather occurs in small jumps and bumps with associated soreness that can occur days later.