Sensitivity to a cold stimulus is a symptom for which there can be numerous causes. In addition, as you have made the reader(s) aware, the area from which the sensation comes is not always readily localized. Receding gums leading to exposed roots can be one cause since enamel seems to act as an insulator against a cold stimulus; clenching or gritting teeth (bruxism) can also lead to sensitivity. Deep decay, deep restorations (fillings), new restorations and some other recent dental treatments can lead to sensitivity,; dying nerves in teeth and cracked teeth are also causes; foreign objects such as fingernails, toothpicks, or food such as a popcorn hull, etc., stuck between teeth or between a tooth and gum can lead to sensitivity as well. Sensitivity that does not go away can indicate irreversible tooth-nerve deterioration, except in those cases where there is root sensitivity as mentioned above. Such slowly-dying teeth can give off pain signals that are difficult to localize. If due to recent dental treatment, the sensitivity will reverse itself if the nerve is healthy.

So, as you said, it could be tooth #3 that is the culprit, and 4 and 5 may be just fine. You dentist can test the teeth to see which tooth it is that is causing the problem and recommend treatment. Sometimes, though, testing may not reveal a single tooth to treat, in which case your dentist will probably recommend waiting for some period of time, usually a few days to a few weeks, and test again. If the nerve of a tooth is deteriorating, it will eventually reveal itself clearly so that treatment can be done on the right tooth to relieve your discomfort.