How many weeks?

I have an appt with my doctor March 7. Until then I'm guessing at how many weeks I am since my periods have been irregular. My last actual period was Dec. 12 but I had 3 days of spotting starring Jan. 4. I am not showing and I just started having nausea and heartburn a few days ago. So I feel like the 7 weeks is a better guess than the longer one. But I guess it could also be neither of these? Any thoughts or advice?