Hello there!
Your situation does not sound worrisome at all. It's completely normal to see a minute amount of blood after having strained to pass a stool. Was the blood bright red? I'm assuming you didn't see any after that? Hemorrhoids can also cause some bleeding during/after a stool. Some people don't even realize they have them.
It sounds like anxiety may be an issue for you. If so, please stop by our anxiety forum, there are some super folks there who could help you, both by giving you some recommendations, and some support:
http://www.medhelp.org/forums/show/71?camp=msc
My unofficial opinion is that I don't see any reason for concern. Of course, it's never a bad idea to ring your doctor's office and run it by them, just to put your mind at ease. The doc may want to see you, or may tell you that unless it happens again, he/she isn't concerned.
If indeed you have anxiety, it's common to catastrophize about your health. Any small, insignificant symptom/sensation/finding will be made into a terminal illness in the anxious mind.
Very best to you, take care!