Watch running a bit slow

[sfrolex]

I started timing my watch to www.time.gov.

I started almost one week ago, actually 6 days and 12 hours ago.

For the first few days, perfect time, to the second.

Then over the last few days, it lost a little time. Now it's about 3 seconds slow. I'm wondering if my behavior wearing it factored in. Some nights I sleep with it, some nights do not. Some days I am more active, some days not, etc.

Is this normal? What's the typical time difference over a week or month?

I have the Sub Date