Have a medical condition that will allow you to qualify for only a third class medical? Has your medical certificate expired or been denied? Just because you don't have a second class medical doesn't mean you can't provide flight instruction.
According to FAR 61.23, a third class medical will suffice if you are exercising the privileges of your flight instructor certificate while acting as pilot in command (PIC) or as a required flight crewmember. In other words, you can do the same type of flight instruction with a third class medical that you could with a second class medical.
If you don't have a current medical, you can still provide flight instruction as long as you are not acting as PIC or as a required pilot flight crewmember. You can't act as a safety pilot because that would make you a required flight crewmember, but you can instruct someone who is at least a private pilot, is current, has a medical, and is qualified to fly the aircraft you are instructing in. And yes, you can get paid for your flight instruction services. For more information, read " Teaching without a medical" in the June 2003 AOPA Flight Training.
October 30, 2006