R.,
It looks like you have gotten lots of advice here. I would add that at 4 months, my first-born started screaming, too. This went on for months. You know, they can be cutting teeth long before you see any of them. Also, symptoms of a cold can be related to teething. This includes pressure in the ears, which can be extremely painful. Do you have a baby swing? We could not have made it without our Graco swing! I would hold him and co-sleep also. Snuggling does wonders. Also, if you still have any breast milk, I would "put him on." This is a wonderful drug. Regarding Motrin, I think your baby is a bit young for that. I think they prefer 6 months of age, so you might check on that. Motrin does wonders, though. For us, it works better than Tylenol. Also, there are several homeopathic teething remedies available. For such a young baby, we had success with Boiron brand Chamomilia. Hyland's makes a good remedy also. This will pass, though it is intense right now.
Amy