Linea Nigra? already?

I'm 5 weeks and 5 days with my first pregnancy and fair skin. I noticed 3 days ago a darker line from my naval down and attributed it to my bloated belly and tight pants. However, over the weekend I ensured I wore loose fitting clothes for maximum comfort and the line is still there. The research I've done for the linea nigra says it generally shows (if at all) around week 18-22 and typically for women with darker skin. Is anyone else experiencing this so early and especially with quite fair skin?