Does anyone know if this is normal?

I know a lot will say its urine but I've been keeping an eye on my discharge and stuff when wiping and usually don't see yellow on the tissue. I've noticed from around 20 weeks I've been having yellow tinged tissue everytime I wipe now. I am currently 29 weeks pregnant now. Is it normal? I don't have any itching and there's no smell to it. I have notice with this pregnancy, I do hold a lot more pressure in my belly and down there. Also have backache, which I never had any symptoms really with the others not even when I got to 40 weeks.

Could it be my amniotic fluid leaking slowly?