How early can you notice pregnancy symptoms??

So with my first, I noticed that I was extremely thirsty, tired, and had headaches the week before I got a positive. We were trying and I was looking for signs though.

I started taking the pill in the middle of August and I guess my body has been adjusting so my periods have been crazy. I THINK I was ovulating last weekend when my husband and I had sex and this week I have had a horrible headache, so thirsty, super tired, dizzy, nauseas, vomited once, etc. No positive test yet since I should only be about 6dpo. Would it be too early to be experiencing such severe symptoms though?