Day 67 cycle BBT question?

I am now on day 67 of this cycle, I ovulated on day 54, 55 or 56. I don't know which day because I had a stomach bug and it gave me false high temp readings. After my sickness my BBT was up so I did ovulate around this time. I am 12, 13, 14 or 15 DPO, I don't know because of the fever. My question is this morning I took my temp and with been sleepy!!! I thought the reading was invalid I must of been seeing double LOL. I took it again and it was 36.40 which was a drop from 36.60 could this be an implantation dip or could it be a false reading as it was my second one even though I took it straight after the first one. Or is it AF arriving GRRRR. Please someone answer, sorry for it been so lond winded. XXX