Symptom of pregnancy?

My fiancé and I are ttc baby #2. I am too tired to explain the while thing, but let's just day there is definitely a chance I could be pregnant. Yesterday, I had a sudden backache out of no where. All I was doing was walking 5 feet. It lasted a minute or two and then was sore the rest of the night. I was ready for bed by 830 last night although it wasn't until about 10 that I fell asleep because my daughter kept me up. But then I slept about 7 hours, which is good for me. By time 2pm hit today, I was super tired. It's hard to even keep my eyes open. I'm only 6 dpo. Af isnt supposed to start until 9 or 10 more days from today. I have read online that a backache could mean implantation. Is it true? Could I be pregnant?