Well I'm Almost 3 Months Late On My Period And

Well I'm almost 3 months late on my period and I've been having lower back pain stomach pains and I've been very nauseated at times I'm very tired at times more than usual I tend to use the bathroom more often than I used to and every test and I takes continues to come back negative I've been to my family doctor that was also and negative urine test but I just feel like I'm pregnant like I just I don't know and I've been having yellow mucus stuff like coming out also I get knots in my stomach what's going on