What is going on?!

Hi ladies, I'm a mother of two in my late 20's. My Husband and I thought we would try for one more after my last period - my last period was on the 25/08/17 so today I'm on day 76 of the same cycle!!! I've had all negative test and negative blood test. My period has NEVER been this late EVER! My cycle is usually 32-42 days..on day CD 68 I had spotting was more of a brownish colour but still negative test. Has this happened to anyone and they've been pregnant? Or even if it's happened and it was something else?