penis craters?

i'm not sure if they're called craters or not, but that's a term i found while searching online. so i've basically had about two or three "craters" on my penis since i could remember. they look like a fold in the skin, but when you pull the skin back the part underneath is almost like a pocket. when i squeeze them, they are similar to pimples because i white head comes out. there are other small ones as well. these craters are only generally where the shaft and head meet. the latest one i have looked at was the largest one. when i squeezed it the white head came out followed by a little pus and then blood. this is the worst so far and now i am worried. online, the crater were said to be related to ulcers and syphilis so i want to get some more opinions on what this could be. i also plan on seeing my doctor as soon as possible to ask about this problem.