Tragically weak arm rotation

[EasyRhino]

Man, I've only been lifting for a few months, and I already hurt something. I feel like such a doof:

1. It began a couple of weeks ago. Between NROL workout where I was doing dumbbell push presses (fine) and two days later doing DB incline presses (not fine).
2. The workouts felt fine. And no pain or anything else was memorable in between them. So either the workout strained me stealthily, or I had the proverbial injury while picking up the newspaper.
3. There is no pain. There is, however, weakness in my left arm/shoulder. I first noticed it by being virtually unable to do push presses with my left arm. Didn't hurt, but I just lost all power when my hands lowered to around ear level. I did some debugging on myself after the workout, and learned that my ability to do a single arm external rotation with my left arm is just shot. A 4lb pink dumbbell is a real struggle.

Flexibility seems okay if I manhandle the arm backwards, but I can't really get the range of motion otherwise, it's like the muscle isn't strong enough to counteract the regular tightness opposing it.

9) When doing a press-like motion with zero weight, lowering my elbows to the lowest point of their ROM (hands below ear) will make a 'crunchy' feeling around the back of the shoulder (I usually get this, but it's more pronounced on the left side), and then the strength goes away.

I don't have the pink dumbbels handy now, but a front lateral raise seems extra difficult as well.

6) No radiating to other body parts.

9) When doing a press-like motion with zero weight, lowering my elbows to the lowest point of their ROM (hands below ear) will make a 'crunchy' feeling around the back of the shoulder (I usually get this, but it's more pronounced on the left side), and then the strength goes away.

I don't have the pink dumbbels handy now, but a front lateral raise seems extra difficult as well.

10) I'd like to get the strength back.

11) No injuries previously (again, I'm a noob)

12) Hasn't been getting worse.

Some googling implies that my supra or infra spinatus have bonked:
http://www.exrx.net/Kinesiology/Weak...#anchor3503966

So... what do I do? Rest it and avoid working it? Remedial exercises to strengthen it? Wallow in self pity? I can handle the last one.

[UConnJulie]

Weakness that comes on without any provoking injury is always something to get checked out in person in my opinion.

[EasyRhino]

Thanks Julie, I suppose I knew that was the commonsense advice. I guess I was just working under the assumption I had provoked it somehow... I just didn't notice it when it happened.