My wife and I are completely new to raising chickens. We purchased a Cornish Rock that is now about 18 days old. When we first got him we think he developed pasty butt. We cleaned this up and he seemed fine after about a day. However, over the past few days we have noticed a swollen protrusion under his vent in the intestinal area. He eats a healthy amount and is growing very rapidly (he is the biggest of the group). He lays around a lot more than the others but he always has. He doesn't appear to be in any pain and when he wants to he can get right up and run around with the rest of them. Should we be concerned? Any input would be greatly appreciated.