What Causes Delay In Menstruation Other Than Pregnancy?

hi, i'm 19 yrs old. i'd been getting my periods regularly till the last july. after that i didn't get period in august. between july and august, i suffered from severe viral fever & viral arthritis(i've not medicated for arthritis). i've consulted a gyno who prescribed "primolut-n" and the following september and october i got my periods. today is my due date for getting period, and i haven't yet got it. what do i do? is there any major problem?