Baby's heart rate dropped

Tessy • I am 31 and ttc for about 3 months with bf of 7 years and 2 months. We both already have children from previous relationships. I have 2 boys and he has 2 girls but we want a child of our own.
I went to the Dr last week when I was just 5 weeks and heart rate was 90 bpm went to the Dr yesterday and baby's heart rate was 78 bpm...my bf and I had gotten into a really bad fight and I went for a walk to calm down...this happened on Sunday night my appointment was the following Tuesday....has anyone else experienced this? What was your outcome? Is there anything I can do or eat or drink to bring up baby's heart rate? Please help I am so scared of having my 3rd miscarriage just in this year I really want my baby to survive