I recently (a week ago) got side-kicked with a heel in my sternum pretty hard, enough that it knocked me down (I weigh 215 lbs). Needless to say it was very painful and a week later it still kills if I try and do any pushups or move certain ways. There is no external bruising or anything; it's just very uncomfortable. Any idea how long this will take to feel better? Do I need to go get it checked out? Anything I can do to speed the process?
I occasionally get what I think is a costochondritis flare up, so I can sympathize.
First: If you have any doubt on getting it checked out, even if you think it isn't that big of a deal, it is probably a good idea to do so. There are a host of things that a bunch of people on an internet forum won't be able to tell just by your description, and you shouldn't listen to our advice over that of a professionals anyways. So best practice: if you are still having pain a week after, it is probably a good idea to get it checked out.
Second, at the risk of being somewhat obvious: It will take substantially less time to heal if you just let it heal. It is amazing how many things can slow sternum healing, including doing things like pushups or even some stretching. Certainly things that activate the surrounding muscles, such as pushups, should be avoided.
The standard advice for most injuries applies: use ice and let it rest. Make sure you are getting enough calories (if you have been eating anything less than maintenance, stop that, and consider going beyond maintenance until you are recovered). Then ease yourself back into working out, generally starting with stretching until you are recovered. Avoid sparring or anything that is likely to get you reinjured.