It's likely guilt since you only feel it when you focus on it, and it's intermittent, not constant.
When we answered your question, we explained that your risk was very, very low, if you had one at all.
If you can't let it go, why not just test? Find a clinic or a Planned Parenthood and just self pay so it doesn't go on your insurance, and test and put it to rest finally. You can be sure it will be negative.