NOT trying to teach you to suck eggs here, but do the common sense thing.

GET TO THE DOC'S!!!

IF you've pulled a muscle, then okay. A few days or so off to allow the inflammation/pain to subside and you're sorted.

IF you've torn a pec, you're potentially a disaster waiting to happen. And here's why.

You're not too sure what you've done, so you doctor yourself by telling yourself to take a few days off from training. You go back to the gym, load a reasonable 200lbs on the bar, settle in for a nice warm up set and BANG. Your pec tares off the tendons and the bar comes crashing down on your chest.

You may THINK I'm over dramatizing things a little, but if you want an example of what a f**ked up chest looks like after a torn pec injury can do for you take a look at this:
http://www.shoulderdoc.co.uk/article.asp?section=898

Or go and Google the injury for yourself and see what you find.

FINGERS CROSSED, I TRULY hope that all you've done is tweaked it and it's paying you a reminder to be more careful in the future. BUT, IF you have done something a little more concerning, isn't it better to be safe than sorry, Mate.

I GENUINELY do NOT want you coming back on here in a couple of days and reporting that you've torn a pec, or a tendon, or something. I'd MUCH prefer you to come back on, tell me to go stick my advice because you went to the doc and all it turns out to be is a muscle tweak and I've cost you a few $$'s in doctors fees.

Just trying to support a brother who KNOWS what he NEEDS to do, Mate.