No sort of birth control is 100% effective. That being said, if it is as you describe, your chances of being pregnant are slim. You've taken tests that are negative, so why worry? Suggestion, if you're not ready for "that" responsibility, then add a "raincoat" to your pregnancy prevention routine.
Should I be worried? I had unprotected sex recently. I am on depo and I have taken three pregnancy tests all saying I wasn't pregnant but I can't stop worrying, I need a real person's reassurance please.
If you truly want reassurance then i would suggest you see a Gynaecologist for a blood pregnancy test (hCG) This is 100% accurate. Hopefully you'll get the answer you want......