Shoulder pain help!!!

Please read whole thing:

Sprained my shoulder I think. But I'm trying to figure something out.

Is it possible to sprain your shoulder and it not to have symptoms (like bruising and pain) until a few days after?

Long story short:

I got shoved roughly (read purposely) against a car seat (me in back, person in front) on the shoulder that's hurting. But there was just a little pain that went away right after.

The pain started a few days later probably because I was lifting mildly heavy boxes.

My question is, is it possible that my shoulder was sprained when I was pushed and it didn't show until lifting the boxes???

Or would I have felt it right away and it would stay hurting?

It's also possible it's just from the boxes, I'm not sure.