I would take him to a groomer right away. They may need to give him a haircut if the knots are too bad, but it'll grow back, and you can make grooming a special time for you and Pepino.

The knots and tangles are probably very uncomfortable for him, so that could be why he's not feeling great. Take him to a groomer, and then you and Pepino can start again on keeping him beautiful and more comfortable!