If you have regular periods and are 30 years of age or less, the general recommendation is to attempt pregnancy naturally for one year before exploring fertility treatment options.
Menstrual irregularity, on the other hand, is a clear sign of irregular ovulation and would be one reason not to wait, as most ovulation problems can be corrected with medication.
For women who are over the age of 35, it would be reasonable to do some preliminary fertility testing right away. This would ensure that there are no problems that need to be treated immediately, given the limited number of years left for child-bearing.