Is There Safe Dates To Avoid Pregnancy In Case Of Irregular Periods?

Our baby born on 11/11/2010 , After that my wife had periods on 23 december, after that we meet on 10 feburary. she dosent have periods after 23 december.

Will you please assist us?

One more question , fartilization done in between 10 to 20 days from first day of period Or it comes every month even if periods are not regular.?



Thanks.