5 days late and then only light brown spotting, is this normal?

Last month I had a bit of a pregnancy scare after being 7 days late but my periods can be irregular anyway, this month I have been 5 days late so I thought not to worry as it is around the same time as last month. I went to the toilet today and noticed there was a bit of brown discharge (obviously been checking when wiping to see if I have came on) anyway I didn’t think anything of it and just sorted myself out as usual when coming on but every time I have changed my tampon there’s only been a little bit of brown discharge and I’m one of the bitches that only get a 3 day period so normally for the first day and a half I’m really heavy. I have googled it and it says implantation bleeding is a possibility but I need to know if there’s any other reason for it?? Myself and partner are not trying to conceive and is totally out of the ordinary😕😕😕 I have had all the symptoms for my period like cramps mood swings and sore breasts but this is so unusual I am getting worried??😞