12 wks can't detect baby heart beat

Hello ladies, I'm 12 wks now. Went to doc and they couldn't hear baby heart through Doppler, she had to do tummy US to see baby and said he/she is fine....but  lately I have been feeling very weak and want to eat like every two hrs. And then dizzy,headache,  lightheaded, heart beats fast and sometimes shaky hands. Is this normal for 12 wks to have these symptoms and then can't hear baby heart. Anyone else feeling same. I am very scared this is my second and it wasn't this bad with my first. Pls help! Share your experiences too.