Blood when wipe 3/4 dpo

[WonderVibe]

I track my bbt using natural cycles and they think I ovulated cd 17 - cd 18 with most likely being cd 18.

I'm currently cd 21 so either 3 or 4 dpo

I've just gone to the loo and have light red when wiping

I'm just wondering if anybody has experienced this and what the cause might be as I know it is too early for implantation bleeding

Thanks

Following as someone who also had this this cycle at 4/5dpo. Lasted 2 days and never became heavy enough to do more than brown spotting on a pad and has now gone completely. My temperature also dropped and has stayed pretty low so think it may have just been a really unwelcome early period that was super light due to being so early 😞