Don't beat yourself up over it. I understand the frustration but sometimes life just gets in the way. I try to make up for the off days on weeks when the weather is nice. Two weeks ago, I bike commuted all 5 days. Last week, I rode 3 days because I got rained out one day and had a doctor's appointment another day. This week, Monday was a holiday, so I've already missed one day (although I rode today).