What's happening...

I have a normal cycle, or that's what I thought... It's been normal for the last 2 years(after being on the depo and not having a period for 4 years after I came off it) I always come on around the 1st of every month. This month is the first month iv been ttc taking vitamins and glow said my fertile week was the week starting like the 11th July so for the week me and my fiancée had sex every other day, however I got 4dpo (having bad stabbing pains in my right side, back ache and even one stage was sick) then started having spotting. That then turnt I to heavy clots and now keeps stopping,then starting again.. It could be really light and nothing there, then me feeling like iv leaked, ( although I haven't) but when I go to the toilet and wipe it's heavy :/ iv now been bleeding on and off for like 8 days :/ Iv taken pregnancy test all come back negative..  Does anyone know what could be happening.. I'm not sure what all the fancy terms for things are and I do have Pcos BUT even though I have it my cycle has been spot on every month ...