Late in cycle ovulation!!!

Nu
Asalam alaikum ladies. I accidentally posted in the faint BFP room when I was trying to post here. 
I usually ovulate around cd 13-15 but this month i got a +opk today on cd 20 out of a 28 usual cycle!!! I have never had such a late positive opk. Has this happened suddenly to anyone before. Oh yah this is the first month I'm using cheapy test strips that I got of ebay so I'm not sure if this has anything to do with this late detection of LH!!! Please help