In some guys this goes in cycles. I am 54 years old and I stll will tend to have one or two episodes like that a year. They don't nseem to last as long as they did when I was younger, but it still occasionally happens. It's a normal fact in a number of men and is nothing to worry about. When I was in college I had a period where 3-5 times a day wasn't enough. It seemed like it lasted forever. I never figured out what caused it because there was no particular event or time of year that triggered it. Just do your best to gain some self-control and "relieve" yourself enough in your free time to minimize the annoyance.