Conversion Rate Drop - Cookies Issue? Help!

I own mini niche Amazon Affiliate Website almost 1 year, in the last 6 months I had nice earnings but in the recent week since I updated some plugins and also the Wordpress version, my conversion rates dropped systematically! Day 1: 7 Sales, Day 2: 4 Sales, Day 3: 2 Sales, and now it get to 0 SALES! (First time that I have day without sales in the last 6 months). My traffic & my clicks to amazon still the same but no conversion! I checked the articles and the links and all of them are working fine with my affiliate tag. I asked Amazon support and they say that on their side there isn't a problem.
I think that the problem is that my website isn't planting / injecting cookies into the visitor's browser and that's why there is no conversion while all the other stats (Traffic) remain the same! But I'm wondering what can cause this issue.. which plugins are messing with cookies? Maybe w3 cache? Or any other cache plugin? Please help me with this ...

Up?................

Try uninstalling each of the plugins and see if that helps. If not have a friend buy something from one of your affiliate links and see if that helps.