Very confusing cycle ladies

Hello ladies, I am having a very confused. I am usually on a 28 day cycle at all times, but my cycle was supposed to arrive on Monday but still hasn't said hello yet. I have been having very bad cramps,back pain,no sore breasts as I do right before my af shows up. I also have been a lot more hungry and eating more,very very tired I actually find it hard to stay up. So since I am 2 days late I took a first response rapid result pg test this morning and it was negative. I'm not sure what to think now, can someone help me figure out what's wrong. Also I have hypothyroidism.