130/80 is considered normal for those of us over 50 because our blood vessels are a little less flexible. Your diastolic is within range and I'm a little surprised that you were prescribed BP medicine. Thank goodness for side effects (sometimes).
The systolic the top number varies from minute to minute between 5 and10 mmhg. Coffee or tea (caffeine) can raise the systolic number 14 mmhg.
If sitting completely still for 30 minutes is difficult, you must be normal. Forcing yourself to do so can raise your blood pressure.
158 is too high though the risk of stroke is said to be at 180. More importantly the 158 seems to be an anomaly.
And they want three reading because often the home devices aren't altogether accurate.
I don't think you should be worried at all. But you could get a cardiac consult. I decided to because of my age-- The cardiologist I saw doesn't consider prescribing medication for a systolic under 140 in our demographic.
From 1991 https://pmc.ncbi.nlm.nih.gov/articles/PMC9697712/