Why arent my lines getting darker ??

Danelle

Hi. I’m 18dpo. 4 or 5 days past missed period. I got my first faint line on dec 26. The tests got a tad darker, easy to see, but they’re still light. Boobs have already gotten bigger. Should I be worried? I do know implantation was dec 23. I had cramping. So I know it’s still super early. I just thought the line would be darker after 7 days of positive tests.