Hi, and thanks for your query on eHealth forum!
Usually fingering does not cause pregnancy, even if it has pre-cum on it. However, if you were close to ovulation date, then yes, there is a slim chance. However, since you had two consecutive scanty periods, take a blood pregnancy test which measures beta HCG levels. If this is negative, you'll have to consult your gynecologist to find the cause. Hope this helps. Take care!