When is weight loss concerning?

I recently started dieting. I'm going to the beach in a few months and want to feel confident in my bathing suit.

7 days ago, I started counting calories. I weighed in at 135.

Today, I weighed in at 126. I'm one pound lighter every morning. I've also been having a rough gut (normal for me) and TMI... had the shits each morning. Only once though. Not throughout the day.

I eat 3 meals a day (ex: oatmeal and banana; pizza; bagel w/ cream cheese; yogurt for a snack).

I'm not eating fast food anymore (I used to eat it 1-2 times per week) and drinking more water instead of juice, milk, or soda.

Should I be concerned that I'm dropping a pound a day? My goal is 120

Also, my working-out is minimal. I'm mostly just counting calories. I'm on my feet all day 3 days a week though, and averaging 13k steps those days