girlfriend upset over limp dick

I've been feeling Ill today and out of boredom got myself off a couple of times. So when my girlfriend and I begin to have a sexual video chat showcasing herself I could only get half hard. At this point my head is throbbing and my penis was a little sore from earlier and she realizes the lack of hardness. I was trying to explain to her why and she had a hard time believing me, so now she went to bed upset. I'm not sure how to fix this she'll probably have her doubts that I think she's sexually attractive.