Okay, now I have a better picture of what was happening. So one of the most fundimental rules of giving a proper handjob is that the penis must, repeat must, be lubricated. Remember that the penis is a sensitive area and should be treated appropriately. Now, this can be with any mild lubricant or even hand cream, or if your gf prefers she can use saliva (mixing in some oral sex as well).
For now I would recommend is that you refrain from unnecessarily touching or manipulating the area.Wear loose and light underpants.Wash the area with a mild and bland cleanser like Cetaphil. Pat the area dry with a clean towel. If needed you may apply a topical antimicrobial over the area to prevent an infection.
Hope this helps, and next time have her be a little gentler whilst "rubbing the rod!"
Wendy