My friends have me worried

So I had sex, while I was very fertile, 4 times in the same day, the condom did come off once. I didn't think anything of it, and I didn't for awhile. About 6 days after sex I had a very small amount of spotting and cramps, which I thought was weird looked it up, and everyone says maybe it's implantation bleeding. I still don't believe it. Anyways my breast are very very sore, I almost cried putting on a bra this morning. And my areolas (that's what you call around the nipple right?) Have gotten a lot darker. My friends are all saying I could be pregnant, I don't want to believe it or get worried without cause, my period is not due to start for about another week, should I be worried?