Symptoms but no HCG

Is it possible to feel symptoms before your HCG is high enough to show a positive result? I took a FRER and it was negative but I swear I feel pregnant. I don’t see how these symptoms can be all in my head, but how would I be having symptoms if my HCG isn’t elevated since HCG is what causes pregnancy symptoms?

Symptoms include: increased sense of smell, mild nausea, chills, hot flashes, a weird sense of panic that I had throughout my first trimester with my first pregnancy.