About five years ago I had two root canals done.. and at the time only had one filled. They put a cap on the other cavity because I couldn't have it done at the same time. Well as time went on I never ended up getting it filled and the cap fell out. One day the tooth cracked in half and fell out. I am worried about abscesses, how do I know if I have one or will have one? Its been over two years with no pain and just an empty space. The empty space is on my right side and lately my right eye and ear have been hurting as well as a slight headache.. it could be allergies. Im wondering what you think. Please help!

I'm thinking you need to get yourself into a dentist's chair for an exam and to find out what is going on.

Needed to be in dentist office long before, yes, it can lead to many things, there is most likely parts of tooth left.

I have a tooth that broke at the gum line quite a while ago, and I have had a congested ear ever since. Sort of sore nostril too. Due out in a few days.
Yes, of course the nerves from your teeth and jaw go upward and downward, affecting the entire head, and more.
Years ago I had a cracked tooth under a crown, with an infection going downward, and I had a serious bronchitis that wouldn't respond to any anti-biotic for 10 months, until a periodontist identified the problem. The tooth had to come out and the cough was gone in a few days.
You would know if you had an infection/abscess - sore red gum, possibly swollen too.