In general, herpes outbreaks are usually related to some challenge to our immune systems. A cold, as you mentioned, is often a trigger for those who are prone to being symptomatic. Another very common trigger is emotional stress.
If you are having a lot of trouble with frequent outbreaks, get your doctor to give you a prescription for suppressive antivirals. Generic acyclovir is very inexpensive these days. It and the other available antivirals are very safe for prolonged use.