What Causes Irregular Periods?

I am 30 years of age and have a 6 years old daughter. last to last mth I had the periods twice and last mth it was again normal but this mth till now I have not got my periods . My Period Cycle is of 25 days and this time I am 10 days up the cycle , the tests show that I am not Pregnent What to do , I donnot want another child