Overall "blech" feeling?

I am 18wks today and while there are are some days/times I feel great, I have an overall "yuck" feeling... I was pretty nauseous my first trimester and have low blood pressure so if I don't keep my blood sugar up regularly I can get nauseous easily.  Anyone else experience this?  Or is it in my head / I'm being weak?  I don't remember feeling like I needed a nap every day with my first 2 pregnancies!