Is it normal to test negative at 8 weeks?

I have implantation bleeding (light brown spots on my liner) for 2 days during the correct period (according to multiple apps). Experiencing slight cramps for many days already and a bit of backache now and then. But breasts are not sore or heavy. I tested negative today at 8 days late, do I tell myself this is not the month or do I test again a few days later? My period is usually on time.#pleasehelp #tryingtoconceive #pregnancy