Cycle ovulation question

Makenna

Is it weird that last cycle I got a positive opk at cd 18, and then this cycle at cd 15 or 16? My tests are rising and I assume I’ll get a positive day 15 or 16 (tomorrow or Friday) but I always get a 30 day cycle (usually) is that normal for my luteal phase to differ 2-4 days( unless my period were to come earlier..) help!