Four days late

So... We're ttc without really trying. (i.e. Apart from keeping note of AF & BD we're not 'actively' trying.)
​I'm usually bang on a 34 day cycle but this time no signs at all of AF and currently four days late. 
​Took a test yesterday and BFN.
​Feeling generally nauseous today but not like I'll actually be sick.
​Have had cramp like feelings for past few days but not as strong as AF. 
​Tmi but was constipated for a few days last week (something I've never had before).
​Also had half a glass of wine over the weekend then suddenly felt so nauseous I couldn't even look at the rest of the drink. 
​Any ideas what's going on?
​As I said, BFN yesterday (with a First Response test).