What Causes Inconsistencies In Periods?

i had my period on 20th nov and on dec i did not get one then on jan 05 th i had it again and on 23 rd jan also i had it but since then i didnt get it as yet , today 11 th mar i went see a doctor she said i am overweight and i may have a homone problem , i got married last may since then i had regular periods until dec '09 i moved to doha from sri lanka on june since then i am gaining weight and lack of exersise