I felt like that up to about 16w and then I started feeling better. But now at 32w, I'm feeling sick tired all the time again. Me and baby have been healthy the whole time though.
I'm 12 weeks too and in the same predicament. For the past week I was fine and had tons of energy and now I'm exhausted. Try getting a lot of fluids and rest that might help and as for your back I know my lower left side hurts because my baby is over there so I use my body pillow every night and it alleviates a lot of the pain for me.
I felt like that a lot . I just had an appointment today and I'm healthy and so is the baby if your really worried ask your doctor