Late period....painful cramps..??

I am 17 and my boyfriend and I had unprotected sex two weeks before my expected period...the expected date was December 27th. Starting on the 23rd I started experiencing cramps like I would get with a normal period like as a warning sign that I am about to start. However on the 27th the cramps were continuing and they progressively got worse and more uncomfortable and I experienced a light bleeding but my period did not happen...so like most girls would, I became concerned that I was pregnant and the bleeding was from implantation...so I waited a couple days and the cramps continued but still no period...I told my boyfriend and I cried about it to him and we talked out every possible decision and the pros and cons of each...he offered to get a pregnancy test and I told him to wait a couple more days and then we would get a test...on January 1st I finally got my period...I told him and we were both so relieved. The cramps are continuing during my period because they always hurt more when my period is late, does this happen with anyone else? I'm confused on why there was light bleeding 5 days before my period? And I also read it is possible to be pregnant and still get your period, is it possible that this could be the case because of the light bleeding? I have also not done a pregnancy test yet but I'm considering taking one when my period is over. Would this be a good idea?