I am going thru just about the same thing over here, being that i ovulated jan 6 but had sex jan 4 and i was due for my period jan 20 and it has yet to come took 2 hpt's and they both were negative, it is now jan 25 and still no period but today i had lower back pains, but my suggestion to u will be to go to the doctor
negative tests can definitely be wrong...happens all the time. especially if you tested early. my first two tests were negative and now im almost 23 weeks!! so i would definitely retest in a few days once your late. if you ovulated later than you thought it can easily cause a negative result. also though premenstrual symptoms can be the same as pregnancy symptoms...or your mind can fool you into thinking your pregnant. you just never know! but i hope you are!! baby dust!! xxx