Cramping after achieving orgasm?

Hi,

Right now I am 16 dpo. I missed AF, today actually would have been the final day. For maybe the past week I have been experiencing menstrual like cramping after orgasm, as well as severely tender breasts and some nausea that comes with or with out food. At first I just chalked it up to AF but she didn't come and I'm never late. 33 days on the dot every month. Has anyone experienced things like this? I have also tested and got a bfn. Thoughts and opinions?