5.5 after ice cream is certainly nothing to worry about!
You need a good set of readings over a period.
Do tests daily:
Before bed.
Shortly after you get up.
Just before a big meal.
2-3 hours after the meal.
After any lengthy period without a meal (5-6 hours).
After a month, look for:
Regular highs (more than 8) in the morning (possible dawn phenominum, try having supper).
An average reading north of 7.
Double digit after meal readings, (Look at your diet. Pizzas and pastas are nice, but very very bad).
Unexplainable surges in sugar levels (no exercise, snacks, month issues, drinks etc).
If still concerned, see your doctor.