I don't know.
My last period was really weird. Very light and very short. And also earlier than expected. I thought it was just begging weird and was really depressed thinking I'd missed ovulation.
At my scan she dated me as a week ahead. And i thought it'd be a week behind. Because i thought i ovulated at least a week and a half after my period according to my bbt and ovulation test.
So when i counted back from wherei thought i was...i guess i might have conceived just before my last period? And that it wasn't even a period. It was really light, the majority was over after one and a half days, the rest very light spotting i didn't even bother with my cup.
But then i had what seemed to be an ovulation afterwards according to bbt graph and ov tests i took. But who knows, maybe just heard to interpret.
But it might just be stress. I was so stressed about trying to read my cycle after having come off my pill. And at the thine i was feeling so low. But then to me if she's dated me ahead by a week it's the only explanation cos me and the bf only had sex once that week. It was pretty crappy. We were both dead tired from work, and had no energy. i was depressed about but getting pregnant at the time (or rather just feeling like i couldn't read my body)
Anyway i for my bfp the day i thought my next period was due had no symptoms beyond usual period symptoms such as bloating and bigger boobs.
So it's a possibility. Or it could just be a weird period. It happens. Try not to read anything into it i wasn't even hoping to be pregnant at the thine, is given up and just thought to hell!
Otherwise you just torture yourself every month.