AF yes AF no I need to know

So my af suppose to start Dec 21 but she didn't show and I'm always on time... my back has been killing me with a lil cramps... I feel like I'm about to come on....I keep going to the bathroom just to see but nothing.. on top of all that I had surgery Dec. 8 so maybe that's why I'm late idk but I need to know something.. I took a pregnancy test and it was negative now I'm just a sitting duck I don't know what to do