I tested four times negative to pregnancy when I...

Normal period (Menstration):
The normal period occurs every 28 days ( the normal average is between 21-35 days) and stays between 2-7 days in the normal average.

How much blood come down during normal menstruation ?
The average person loses between 30-40 milliliters (2-3 tablespoons) of blood during menstruation. 

Spotting during period time:
First of all, spotting is a small amount of blood shed during the menstrual cycle, but not enough to be considered a period. Sometimes it signals the start of a period, but it may occur throughout the cycle and it can also be an indicator of pregnancy, a sign of stress, or a symptom of many health issues. So if the your symptoms did not improve, it's recommended to visit a specialist doctor (Gynecologist) for further assessment and management as the treatment depends on the cause.

Causes of spotting during period time:

• Stress and anxiety
• Pregnancy
• Birth conrol pills
• Thyroid problems
• Polycystic ovarian syndrome
• Menopause
• Cancer
• Other causes

Recommendation:
It's recommended to visit a specialist doctor (Gynecologist) for further assessment and management.