Late on AF!! Please reply!!!!!

Took a test 2 days ago it was bfn.. i heard sometimes its hard to see a positive if u have pcos to do a blood work to get accurate answers maybe i saw a faint not really sure.. i have no cramps of af but im bloated sore boobs and for some reason i cant go poop :( i have gas also have CM what can this be please help me out are these signs of af showing up or preg??