Why does this happen to my cookies?

The first time I had baked chocolate chip cookies, they turned out great, soft and chewy. Maybe a bit ery, but that was ok. That was 2 months ago. Now I try making cookies the same way and they turn out hard. So, I used 2 sticks of er, since I normally use 1. I doubled all the ingredients, too. They turned out ok, but they kinda stuck to the pan. I thought the er would make it not stick. So I added oil to the pan, and the cookies flattened a lot, and turned out hard and crispy. Then I looked at the recipe and they said use two large eggs for 2 sticks of er, so I add another egg to my cookie dough, because my eggs are small. They turned out like dry cakes when I took them out. Then I tried making another batter. This time I put 1 1/2 stick of er, and 2 eggs. Since the recipe said use 2 large eggs for 2 sticks of er. I didn't have "large" eggs, so I reduced the butter to 1 1/2 sticks. My cookies still stuck to the pan. Why does this happen? The first time I baked cookies, They turned out great, and they also didn't stick, and all I used was 1 stick of butter with no need to grease the pan. Can somebody tell me why this happens? How is cookie dough suppose to look? Is it suppose to be really thick? Thanks.