Unsure

I am approximately four days late for my period. I have been slightly irregular for the past six months...but took a home test just in case. The test was positive, but I took the second one a few days later (just to make sure of the results) and it was negative. Has this ever happened to anyone before? I am going to call my OB-GYN in the morning, but can't stop worrying right now. I have also been having some nausea and my breasts are more tender and sore than they usually are before my period. I would appreciate any response to my question. Thank you in advance.