I got my periods since 8 months back,what medicine...

what is the possible causes of missed periods ?
1. pregnancy ( if you sexually active ) 
2. Hormonal abnormalties 
3. medications side effects such as Medroxyprogesterone acetate
4. stress
5. Obesity
6. Thyroid diseases
7. gastic system disease (wheat allergy)
8. ovarian cysts 
9. malnutrition and low weight 
What to do next ?
- if you have been sexual active recently , do home pregnancy test and if its positive , consult an OBGYN 
- if you havent been sexually active recently , consult an OBGYN doctor first , and treatment options are usually the following : in case of productive hormonal changes , doctor may prescribe medication to correct hormones imbalance such as duphaston , which you should take a pill every 12 hours for 5 days  , on the other hand , in case of thyriod hormone abnormalties ( usually accompanied with other symtpoms ) , doctor will prescribe medication such as Levothyroxine , and in case of other chronic disease such as ovarian cyst or other disease , doctor may need advanced examnation to determine the causes and treatment pathway 
Needed medical examnation :
- clinical examnation  ,productive system ultra sound  , hormone levels including FSH / LH / TSH / PROLACTINE