Well first of all I am a big supporter of the cry it out, however, if your son is upset for teething (or sickness) reasons, you should not let him CIO. You should comfort him and hold him and whatever. Give him something for the pain and be with him if that's what he needs.
If it is not due to sickness/teething then you should probably try bumping up his feeding. Does he eat solid foods yet? If not that's fine as 6 months is the recommend age, but since he's so close, he may just need that extra kick. Start out with rice cereal and then move to oatmeal if he's fine with the rice. We would give my 4 month old a bowl before bed and that helped him sleep through the night. Honestly, I would at least try attending to his teething and eating needs before going back to the CIO method. You want to make sure that it isn't any of the above issues before you leave him to himself.