I just heard this in conversation among my friends. Is there in difference between to say every time and every single time.
There's not really any difference in meaning, only in emphasis.
When you add the word single, you are intensifying the emotion with which something is said, whether that be frustration (as in the first example) or elation (as in the latter):
Every time we plan a picnic, it rains.
Every single time we plan a picnic, it rains.
Every time I go on a date with Carol, I don't want the night to end.
Every single time I go on a date with Carol, I don't want the night to end.
In your usage
is used as an intensifier to bring attention to how often something happens.
It is the same as saying
Each and every time we plan picnic, it rains.
Whenever we want to have a picnic it rains.
Strictly speaking, it probably doesn't rain when you are planning a picnic, but when you are trying to picnic.
Each and every time we want to picnic, it rains.
Whenever we sit down to have a picnic, it rains.