Suggest Tests To Confirm Accurate Pregnancy Details

I'm 36 years old. And have been having my periods on time past 3-4 months. I never been late before. And first time I am. My cycle is of 25 days. I had my period on time on the 16 dec and my beta hCG sub-unit came 2000+ and doctor said I'm about 5 weeks. I was sure I conceived between 25-30 dec. Is this test super accurate? Coz I thought I was 2-3 weeks max. Please help!!Also on the 8th dec before my period I had protected sex with condom. Just 2 days after ovulation was over. Is there a chance I got pregnant this way??