first trimester or second?

I posted before about how I had three ultrasounds and two of them had similar measurements that would put me at 14 weeks now, but my last ultrasound says I'm 12 weeks... I don't trust the last ultrasound for several reasons but regardless my doctor just changed my due date instead. My old due date was September 13th and this new one is september 26th... I'm more inclined to think this last ultrasound wasn't accurate rather than the other two since I heard hear beats at both of them and you can't hear a heart beat until 6 weeks minimum. ANYWAY! I can't figure out if I should assume I'm still in my first trimester or on to my second and I feel weird when people ask me because I really can't answer it. It seems so trivial but dor some reason I just can't get it out of my head. Any advice?