“I've had this song stuck in my head for two days!”

You heard a song two days ago, and since then you've been thinking about that song over and over again. You complain to your friend:

I've had this song stuck in my head for two days!

(someone) has had (something)

You use "have had ___" when you're telling about something that you started having in the past, and you still have now:

I've had these shoes for over 10 years.

I've had a headache all day.

If you say this instead:

I had a song stuck in my head for two days.

it means that the song was stuck in your head for two days in the past, but now it's not there anymore.

this (person / thing)

In casual conversation, you use "this" instead of "a" when you want to start telling a story about something. Describing something as "this ___" shows that you're talking about a particular person or thing, not just any one.

Using "this ___" suggests that you're going to say something else about the subject. In the example above, it means that you're probably going to say the name of the song, or try to sing part of the song.

have (a song) stuck in (someone's) head

When you "have a song stuck in your head", it means that you keep thinking about the song and can't stop playing it over and over in your mind.

The word "stuck" means "not able to get out". Some other ways that "stuck" is used include:

• get stuck in traffic
• be stuck between ___ and ___
• get stuck in the mud
• (food) gets stuck to the frying pan

To "have a song stuck in your head" is a continuing situation. If you want to describe how the situation started, you say that you "got a song stuck in your head".