Hey, Rafal. I've never heard "miking" before. This might be British English. In the U.S. we would say some of the following in a causal way: 1. I've been slacking off... 2. I've been lazy... 3. I've just been chilling... 4. I've just been hanging out... Hope this helps you!

"I was slacking off all day." That's just one expression

A funny one that we say is: "I have just been farting around all morning. I need to focus and get some stuff done."

On a more colloquial level: "I can't seem to get my butt (the 'a..' word is censored) in gear today." There's others but I'll behave myself on italki.

"milking it" refers to when you have a task, and your taking as much time as possible. For example the job should take an hour but your still not finished. Maybe standing around talking or smoking. I've heard it often in US among workers in factories for example. "I've been miking IT since morning but NOW I have to move my ass."