Mouth What causes these white spots, plz

[sandymelon]

My Guinea Pig has recently developed white spots on his lips. These spots don't seem to be swollen, is this calcium related? He's got a good appetite and a good mood. His recipe is sun-dried timothy and occasionally he is given green peppers/lettuce or corn leaves (not too much each time). A month ago his lips didn't have this noticeable white color. Any advice would be greatly appreciated, thanks a lot.

 

[sandymelon]

These white spots are becoming more and more noticeable. They started appearing in photographs two weeks ago, but hard to notice