What is your height & weight ?
Is this long period for the first time?
Do you have poorly developed secondary sexual characteristics?
In medical terms this is called OLIGOMENORRHOEA.
In some women the pattern of menstruation extends to cycle lengths exceeding 35 days,without any impairment to their fertility.Since this is compatible with normal reproductive capacity within the limits of its own infrequent ovulation,it requires no treatment.However if the cycles are very erratic & infrequent , medical attention is called for.
To be on the safer side you can repeat blood pregnancy test.
Hope this helps.