My period is usually 7 days heafy and on time well the last three months my period has been light lasting 3 days and not on time and I have used pads or tampons because I haven't had to does this mean that there is a good possibility that I am pregnant?

No, if this happened one month, then no periods at all, that is a sign, you may be, but also a sign of infection, hormone issue, stress, medication issue and a dozen or more other reasons