I had a period May 3-7. I was intimate with my boyfriend on May 13th. Shortly afterwards, the beginning of the next week my breast started to feel slightly tender like they normally do a week before my period starts. They were tender all that week and the next week on May 28 I started bleeding again. Is this what they call implantation bleeding or is it actually my period?

My understanding of implantation bleeding is that its more similar to spotting than your period. If its like a regular period I would lean towards no, you are not pregnant. But it can never hurt to take a pregnancy test just to make sure.
Do you use any contraceptives?

Implantation bleeding is not as common as people think. Could it be, yes, is it, don't know.

Try an hpt, use first morning urine, it's more accurate, or get a blood test done at your doctors. That's the only way to find out for sure if you're pregnant.

Good luck.

Implantation bleeding it normally brown (old blood) and only dribbles for (the most) two days.
Depending on your cycle, it sounds like you had sex when fertile.

Everything you have is a "presumptive symptom"... which no physician would use to diagnose.

Period.

And if a physician isn't willing to place his or her reputation on the line with this info... well... then how reliable is anyone's opinion?

The reality is now its all about time and testing and waiting. Anything else is conjecture.