Thinking I might be pregnant...

So I had sex November 18th, and 19th, which were the last couple days of ovulation for me, after last months period. A few days before my period this month I started bleeding, but it was just a little bit, and not a bright red. It seemed odd to me, because I never start early. Well after that tiny bit, I didn't bleed again until my actual period date, but my period seemed way off. I was bleeding on and off, so I would bleed heavy, then the next day it would be little to nothing, and same thing the next couple days. I also ended 3days early. A week or two before I even started my period I began feeling so nauseous, it has been waking me up in the middle of the night, my teeth are killing me, I've had constant headaches, everything I smell is making me gag, (a little tmi) I've had so much gas, I'm constipated, and I'm exhausted, all around I've been drained. I took a pregnancy test last night, and it was negative, but I feel like maybe I should take another in a week or two. I'm thinking maybe I am pregnant, and my HCG levels just aren't high enough yet, also causing me to still have a "period"... orrr maybe I'm just feeling bad for no reason. Has anyone experienced anything similar?