12 DPO Symptoms

Can someone explain? 😕 or similar experience? 
AF due the 20th. Regular 28/29 day cycle The only symptoms in the last 2-3 days are random 10-30 min waves of nausea (one happened in line at Target -that was awkward lol) and random slight twinges and pulling in my left abdominal area into uterus. Not really a heavy cramping just twinges over a very very dull cramp. No spotting. I've been tired but I've also been having long busy days so I'm chalking it up to that. Sore boobs but that's normal with AF too. The nausea and twinges is what's different for me... I'm pretty sure I'm out this month bc we only bd at the very beginning of my 6 day ovulation window bc hubby left for a business trip right after. So didn't think I was preggo until now. I took a FRER today. It was negative.