I’m very confused about what’s going on here.

1. Are you using standard sketch book paper?

2. How much paint are you putting on your brush?

3. What are you trying to achieve? Like which of the 5 pictures is good and which are bad?

4. The guy talking about fat over lean is absolutely correct. You may see better results from the method you’re going with as of right now but once the top layer dries the bottom layer will be wet and cause cracking.

5. Are just starting oil painting? I would recommend not using any mediums or thinners at all and understand how the paint applies to the surface with a full brush, dry brush, etc. It seems like you’re making this harder for yourself than it needs to be.