What Causes Red Blister On Penis Shaft?

i recently say a very small red lesion(1-2mm) on the shaft of my penis towards the head of the penis...it never hurt and i never saw a blister or crust over for that matter. ive been looking online and nothing really compares to this. I noticed it sunday night after masterbating for an hour. by tuesday it was barly visible. im worried this could be something bad