I've had a C-10 for just over a year now, I play it at least 2 hours day usually more. Just in the past two months my G and D string break a lot. When one string breask or in about a week and half to 2 weeks I replace the whole set of of stings. But for the past two months I've been breaking the G and D string in 4-5 days. What is causing this- do I need a newbridge piece??

I use d'addario (12 guage PB).

Did you check and see if the saddle have some serious grooves in that particular two strings??

Check THIS out! Its from frets.com.