Why i am still bleeding after 14days?

Treatment 
you should visit your gynacologist who might prescribe to you Nonsteroidal anti-inflammatory drugs (NSAIDs) which is the First-line medical therapy for heavy and prolonged bleeding and may prescrib Oral contraceptive pills (OCPs): A popular first-line therapy for women who desire contraception in some cases may prescrib Daflon 500mg 
how diagnosis is being made 
Complete blood count , Iron studies (total iron-binding capacity [TIBC] and total iron)
Coagulation factor studies  , Human chorionic gonadotropin (hCG) level , Thyroid function tests and prolactin level ,Liver function tests , kidney function tests , Hormone assays , Pelvic ultrasonography
Causes :

• .hormone imbalances
• uterine or ovarian abnormalities
• Extreme exercise or dieting
• Thyroid disorders 
• sexually transmitted diseases
• diabetes
• fibroids
• eating disorders
• endometriosis.

Does thyroid problem affect menestruation ?
The answer is yes, menstraution actually affects menstruation as you migh be having heavy periods, delayed period, bleeding or spotting between periods and sometimes painful periods.

Whats is the appropriate treatment in this condition ?
Well, the treatment should be focused on the cause of the period irregularities. In your case, it seems due to thyroid hormone imbalance, so thyroid problem should be treated and thyroid hormone have to be stabilized in your blood. Afterthat, your menstration will become normal again.

Investigations to do:
The diagnosis is made by taking full history and clinical examination of the patient. Running some investigations including blood investigations such as CBC to check for anemia of infection. TSH, T3, T4 hormones, in addition to an ultrasound of the gland.

Recommendation:
It's recommended to follow up with your family doctor.