Implentation bleeding only happens at least 14 days after conception, usually 2-4 weeks after intercourse. Therefore, bleeding is not an indication of pregnancy and by the time of implentation, a woman can usually test for pregnancy.
Now, as for bleeding a few days afterintercourse use of tampon... those are signs of mild vaginal tears. Remember, "sex" shouldn't hurt and you should never bleed from your vaginal opening unless you are in your period. In your cases this could be the result of small tears caused by lack of lubrication, and of muscle relaxation.
Ask yourselves these questions: Do you feel unconfortable during intercourse? Are you insecure? How do you feel about your partner? Does he know of your insecurities? Did you "fool arround" beforehand to prepare and stimulate you body ?
The problem could be psychological - wich causes you to contract your muscles during sex - you might not feel the pain - but it might make you bleed afterwards.
Now, as for a physical solution. Try having your partner penetrate you with 1 finger, then 2 fingers and so on (depending on the size of his member) until you are fully "horny" - humid, and wanting more. Listen to your body. Try diffrent positions, maybe put a pillow underneath your to support your pelvis during, maybe his penis is rubbing against sensible areas... experiment and explore.
If you are young, the 3-5 days after bleeding could have nothing to do with intercourse and just be related to unregular mentruation that can occur randomly (up to sometimes 20-25 years of age).
If bleeding persists please consult your Dr. !