Steele-Bike,
Just to re-emphasize what riderx said - At this point you should replace all parts:
1. Middle chain wheel if possible. If chain wheels are riveted, you will have to replace the crank.
2. The chain
3. The cassette or freewheel.

Assuming the parts are Shimano compatible you can get a new cassette for around $40. A freewheel is a little more. Chain wheels don't cost too much, but a crankset can run $70-200 or more. If you have an older standard square bottom bracket, you might even be able to get something less expensive. If it is Shimano splined BB, you are kind of locked in. Chain $20-30.

Let this be a lesson to you, Sonny. Replace that chain AT LEAST every 2000 miles even on a road bike. 500-1000 if you ride mtb on a lot of trail/dirt. And clean it every 100 or so or after every dirty ride. You can go a little long on a road bike, maybe 200 between cleanings.
Good luck,
Raymond