Why? :(

So this month was my first month bbt and my first month with a normal cycle length in a while (after depo). I wasn't 100% I'd ovulated due to 2 high temps then a dip to coverline. But I was hopeful as had almost positive on the 2nd and FF put O at the 3rd. Glow said later though. Today my bbt spiked again so I was hoping for the best. Anyway today I started with really light brown spotting. So looks like AF is on her way :( not fair!!! I'm sure so many are in the same boat x baby dust to you all.