HELP PLEASE

Su

Has anyone ever had a negative hcg blood and urine and then ended up still pregnant. We used opk last month to make baby 6. I had some bright red bleeding before period was due now I'm having some brown spotting and my lower back is killing me. Has this happened to anyone and you were still pregnant and hcg blood or urine test didnt pickup til later. My breast are super sore as well. Help I'm so confused.