You don’t have to increase the weight by a pound a week, and you don’t want to unless you need to to get a sense of fatigue. Different people describe fatigue differently, but you should feel something (strain, burning, itching, etc) at the base of the penis where the suspensory ligaments attach and you might have some soreness in this area after hanging. If you are feeling this, don’t increase the weight unless you go a couple of months or so with no gain.
You may be experiencing some skin stretch still and that may take a few weeks at a new weight level until the skin accommodates the increased weight. If you are experiencing negative physiological indicators, I would stay at the lower weight level until your penis adjusts before moving up even if you are not feeling fatigue. You might not experience any gains until you get up to 10 or 12 lbs, but you have to let your penis tell you how slowly or quickly you can get up to this weight level.