Low hCG

I just need some comfort or something. I just found out I’m pregnant this week. I went and took a blood test this morning and was told I’m about 3-4 weeks along. Super excited super happy. My OB called me stating she wants me to take another blood test due to my hCG levels are low and of course I didn’t ask cause I was shocked and ended up going on Dr. Google and besides a miscalculation of date it also could be miscarriage. The only symptoms I have been experiencing is light cramps, tender breasts and nausea. This is my third pregnancy and I have 2 amazing boys and this is scaring me and I am trying to not think negatively but it’s hard.