Any time something like this happens, you should see a dentist. I know you are scared, but the result of not going, is far worse than going. Yes - You could have an infection and without treatment, you could be in for more troubles. If your gum gets infected, it could infect the surrounding teeth.
Teeth are weird creatures. Sometimes you feel some pain and then it "goes away". Here's the thing: It doesn't really go away. It sits dorment and then comes back with a vengance. Tooth decay can sometimes take years to come to light. If you experienced some pain from time to time but ignored it, you are in for a big surprise. Not only a big surprise, but BIG dental bills. Preventive measures are the best approach and will cost the less. Of course there is the alternative,,,,do nothing, all your teeth will fall out and you won't have anything to worry about! I hate to sound so negative, but you really shouldn't put this off any longer.
Check around in your area and find a dentist that specializes in treating people that are afraid of the dentist - Yes, they actually do exist and could possibily put you out or heavily sedate you to keep you from getting scared.
It sounds to me that maybe whatever is left of that tooth needs to come out. Good Luck - I'm pulling for ya!