beginner lifting, shoulder ache?

I've started a lifting program, which I haven't really done since high school.
It's a 3 day split, based on one of Krista's (http://stumptuous.com/program4.html) ...

I've done 6 days of it, so that's 2 weeks.
Anyway, after the 'push' day, with benching, military, dips, etc., I got a tweak in my right upper back, kinda tucked in behind my shoulder blade.
Not a 'twinge', just an ache that I think would feel better if I had someone really massage it with their elbow.
Anyway, so yesterday was week 2 and push day came around again, and I can still feel the ache in my shoulder. During the workout I didn't feel anything, because it's not a movement pain ...

Someone mentioned if I'm benching, I could be not straight on the bench, and am driving one shoulder down into the bench as I push up on the bar.

I've been rolling on the floor on top of a golf ball to get some nice pressure on the aching spot.

Is all this because I use a mouse all day at work, and now since I'm lifting I notice some funky shoulder thing? Or will this get balanced out once my strength is up?

Thanks! :)

Sounds like it could be something w/ your traps, do you stretch? If not, I'll grab some stretches for you to do that might help out.