Hiya!
I totally agree.. you will never know what definately happened...I once had a missed period and thought I might be pregnant but then my period came eventually and it was heavy and painful and I wondered whether I might have been pregnant but there is no way of knowing either way...some of us have pregnancy symptoms very early on and then you hear of others who say, have irregular cycles, who often don't realise they are pregnant for months!.
It's best to put it behind you, try not to dwell on the past but look forward and concentrate on enjoying life!
Take care x