Why would the first few pancakes come out perfect, but only get worse from there?

Ah, the worsening pancake debacle. I know it well. We have all been there, even after training for countless hours to make the perfect soufflé at the Culinary Institute.

The pan is getting too hot.

You should cool the pan with a quick rinse. This will also have the effect of resetting the surface, to get rid of any built-up grime or grease.

Good luck and happy cooking!

Short answer: The pan is too hot. That explains why the outside is overcooked or burnt and the batter on the inside is undercooked. Lower your heat. Your batter comes into the equation too. If you have thick batter the inside will take longer to cook. So you need less heat so the outside doesn't burn but the inside batter gets completely cooked. Because you're using raw eggs, you need to make sure the pancakes are cooked through. Although remote, there is a chance of salmonella poisoning. Salmonella and eggs is a whole another topic by itself.

I put a little cooking oil in the batter but otherwise I don't grease the griddle. The browning is more even (attractive). Keep in mind I am using non-stick. Generally speaking, I don't like non-stick but I do keep a couple pans around for eggs, omelets and... pancakes.

Medium heat is correct. I have a non-stick griddle that covers two burners on the stove. I heat it until little droplets of water "dance" and the surface and quickly evaporate. Just stick your hand under the faucet and flick a few droplets onto the griddle. That's when my first pancakes hit the griddle. After the batter bubbles appear and the edges start looking dry, I will lift the edge to check for the proper brown-ness. For your subsequent batches, you may have to adjust the heat up or down or adjust how long you leave the cakes on the griddle.

If you want to be a little more scientific, you may want to invest in an infra-red thermometer. That will tell you what the temp of the griddle surface is. Most non-sticks should not be heated to more than 450-500 degrees. If it's a PTFE surface i.e. Teflon, overheating may give off toxic gases. Those gases will kill pet birds. If they can kill birds, they probably aren't good for you.

All things considered, lower your heat. When you have the right temp, your batches should come out perfect and repeatable. There is a certain amount of "knowing what's right" that comes with experience.

I can't cook a whole lot but I make some mean pancakes and NEVER have this issue.

My griddle is on 200-250F depending on the type of pancakes I am making (blueberry and chocolate chip are options) and how fast I want the pancakes made. You should have your pan or griddle on and going and hot before pouring your first set. If anything your first set should cook faster because it is on a new surface.

If you are closer to the 250F range you will be flipping quickly (1 minute max on both sides depending on size) but you can still have golden brown pancakes. In the 200F range this will allow you to control the pancakes more but you might have a hard time getting the brown. Honestly for plain pancakes I like to hover around 230F. And like I mentioned before your first batch cooks quickest and the dropping of the batter cools down the surface for the rest.

The last thing I will mention. I don't use grease or any oils. I feel like this is impossible to even out and produce a consistent product. Also I don't want to be unhealthy (my pancakes are almost fat free) and I especially don't want the oils to taint the taste of my round deliciousness. Instead I opt for PAM. I use the butter flavored PAM and there is no oil taste or film on my griddle or pancakes.