So confused....need support please!

So the last first day of my AF was December 18th......for the past 2 days I have been nauseous and have to keep drinking sprite and eating pretzels. Not throwing up, but definitely sick to my stomach to where it is messing up my day and I am on the couch or in bed most of the day. No fever, no head cold, nothing else. Could this be baby nausea already?

Also, when can I test? Myself and my hubby just started trying this month and have had intercourse every day since the last day of AF, religiously. We got pregnant the first month of trying with our first child back in 2013 and had a normal healthy pregnancy. I don't remember being sick so soon.

Took a test this morning and got a BFN, but am I right by thinking it's too early for a BFP already?

Thanks everyone!