Boyfriend doesn't want to open up to me, is this normal or?

There's been a few times throughout our relationship where I ask him what's going on or how he feels about a situation that has happened and instead of telling me, "I don't really feel like talking about it now, just give me a few days", he just shuts down on me, it sort of makes me feel like he doesn't trust me at all. I told him how I felt and all he replied back with was that he didn't want to talk or think about it even though I'm just asking a simple question. How can I get him to talk to me?