Occasional jumps and drops are within normal.  If you find the majority of your readings fluctuate significantly consider any of the following factors that can contribute to erratic readings:
Taking readings outside of a consistent 2 hour time frame.
Using different positions for readings (some standing, some laying down)
The moment during the reading.
Not inserting kegg fully
Taking readings too soon after sex
Significant stress, change in daily routine or travel
Inconsistent hydration
Illness or infection
Presence of foreign substances like vaginal medication, ointment, or lube.