before starting periods have dizziness drowsyness for 1 hr.

Hi,
Welcome to ehealthforum,
It is difficult to comment on the exact cause for the symptoms that you describe without examining you. These could be attributed to the hormonal imbalances or changes to which your body is responding, breakthrough bleeding, ovulation bleeding, implantation bleeding, etc. The exact cause can only be made out after careful evaluation. If you suspect chances of pregnancy, consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). If pregnancy gets ruled out, further evaluation would be done to look for the underlying cause for your symptoms. Treatment as appropriate (based on examination findings and investigations results) would be started to help you control the symptoms and regulate periods. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet.
Take care.