There is no pressure on the shower, how can I repair it?

Hi, I’ve been enjoying perfect pressure in my apartment since 6 months I moved in. But last week, without any particular reason that I know off, the shower stopped having good pressure. First day was a less, the second day a little bit less. Now I can barely take a bath but pressure is stable. Faucets all around the apartment work perfect, the problem is with the shower, hot or cold water makes no difference. I also checked the shower faucet and is working well too. What can it be?