This is what I was able to fine. I copy a part of it for you and listed the link below if you want to see the complete information about cavities.
There are several warning signs that you may have a dental cavity. A toothache or ongoing tooth discomfort are often the result of a dental cavity. You may even notice dark holes on the surface of your tooth where the dental cavity lies. But sometimes your dental cavity won’t have any symptoms, which is why it’s even more important for you to see a dentist every six months. During your dental exam, your dentist will check for dental cavities using a probe and dental X-rays. If you do have a dental cavity, it’s essential that you seek treatment before it spreads. A dental filling will eliminate the problem and preserve the health of your tooth for years to come. More importantly, taking care of your dental cavity will relieve your pain!
It seems to me that even though you may not see any holes you still may have a cavity. I suggest that you do see your local dentist. If you do not have and dental insurance you may wish to get either dental insurance or even a discount for your needs
Here is a link that may help you