Are you due for AF soon?
I had some pink blood on my tissue about 4 days before my AF was due last month. I was excited because I thought it was implantation bleeding - but nope. Hope you find the answer you are looking for.
nickie is right - its very rare to get pregnant have a tubal but not impossible.
The bleeding could be due to anything including vaginal irritation from sex. You can test for pregnancy 2 weeks after unprotected sex but its not likely you are pregnant.
It does happen very rarely after you have your tubes tied (are they clamped, burnt?) I really think it all depends on the method you had to have your tubes tied and how long they have been that way. (I had a friend that had her tubes clamped and she ended up pregnant after 5 years) It could just be spotting from something that is irritated or hormones skipping around. If you are concerned about pregnancy then take a test 14 days after the last time you had unprotected sex. Good luck!