Maybe you could share with us why you have the pulse oximeter in the first place? Do you have respiratory disease? How old are you and what is your medical history?
I have an oximeter...sometimes if it isn't picking up a good signal or strong pulse, the reading won't be accurate. It is always a good idea to keep the probe on for a few minutes to see where the number sits. Maybe your circulation isn't as good as other folks...I know that when my hands are cold and I place the probe on my finger, it will read a low number because the signal will be weak. As my hands warm up, the number gets better because of a stronger blood flow.
I hope this helps...Sunny