So the last few times my wife and I have had sex, she hasn't been as wet...in fact, when I pull out to ejaculate, my penis is not lubricated at all. It happened like that probably three times. Anyways, so today I noticed that the shaft of my penis on the underside is chapped and the bottom of the shaft is red. We have both been tested for STIs. I would love to assume that it is because of the lack of lubrication....is that a fairly safe assumption?