Period Problem

Hi there, just want to ask and seek some advices. If meron dito same case with me. Ganito po kasi yun, dapat po Dec.01 darating yung period ko, until Dec.07 wala parin so nag pt po ako sa bahay and negative naman ang result. Until last Dec.10 wala pa rin yung period ko pumunta na ko sa doctor para magpacheck and ginawan ulit ako ng pt using blood (serum pregnancy test) and it tured out NEGATIVE again. Then the doctor prescribed me a medicine. Pamparegla daw yun 1× a day, nagstart na ako mag take last Dec.10 until today Dec.16 hindi pa rin dumarating yung period ko. Medyo worried na ko. Don't know what's happening? Is this just a delayed period or what? Normal ba na madelayed ng ganto katagal? Ang follow up check up ko is sa Tuesday pa.