Should I be concerned?

Susan
Hi everyone!  Over the last few days, I've noticed that my daughter is feeding less. She is 5 weeks today.  Up until a few days ago, she would spend about 15 minutes on each breast per feeding roughly every 2.5 to 3 hours or longer.  Now, she only feeds for about 10 minutes on one breast and falls asleep or stops eating for about every 2 to 2.5 hours.  Is this something I should call my pediatrician about or have any of you experienced something like this?  She has been steadily gaining weight with regular wet and dirty diapers.