Weird flutter feeling???

Im currently 16 dpo. According to glow af was due yesterday but this is also my first month off the pill so I'm thinking it'll take a few cycles to regulate. No sign of af, my temp is still high and now today I'm very nauseous and fir the first time, I'm feeling these weird flutters / muscle spasms in my low belly/ uterus. The ONLY time I've ever felt these were when I was pregnant with my daughter. I'm still getting BFNs tho. Anyone else felt these flutters and then got a bfp??