Not sure what’s happening??

I came off my contraceptive pill 2 months ago had a period as soon as I came off then exactly 4 weeks later. After waiting a month I started TTC. I was tracking ovulation because I wasn’t sure if I would ovulate so soon after coming off the pill but last month while on holiday I got 2 days of positive ovulation tests. This is where it gets confusing. I was due my period Thursday but started bleeding last Sunday 4 days early and I had one heavy day the next day was very light but the blood was red. I thought there was a chance it could be implantation bleeding but I don’t a pregnancy test the 1st day of my missed period and it was negative??? What happened there so not like me to only have a 2 day period? Has anyone else had something similar?