early pregnancy!

I’m so confused and I need help!! so the first day of my last period was November 18th, and my wife and I inseminated on the November 28th and again on December 1st, I got my first positive on December 10th when I was 9 dpo and 12 days past the first insemination. I continued to get multiple positives with at home tests and doctor test but I went to the hospital today because I was having some pain on the left side of my stomach and it wasn’t going away. They told me I was pregnant and my hcg is only at 600 but they couldn’t find a pregnancy in my uterus. I have no idea how far along I am. I’m not sure if I base it off of the first day of my last period or the days we inseminated. can someone PLEASE help? I’m roughly 4/5 weeks pregnant. Is it too early to find a pregnancy in the uterus?