V.S.
Is she having a BM? She could be gassy if she isn't. You can always contact the dr and ask but as long as she isn't losing weight, she sounds fine. And since she's sleeping ok, I wouldn't worry too much. Kids, yes even babies, go through phases and you have to realize she is growing so she may be eating more at one sitting. Thus reducing the amount of times she feeds. Are you nursing or giving formula? Babies bodies do change unfortunately. My son, when he hit 6 weeks, had horrible gas and had colic. Unfortunately with us, we did not figure out his problem until he was about 3 months old and it ended up being he needed on Soy. Once he was on that, he did great and is still doing great. Now he eats like a horse!!!
My personal opinion is as long as she sleeps and is gaining weight fine and doesn't seem grumpy or in pain, she is ok. Now if starts getting colicky and is still gassed bad, then I would speak with the dr. If it completely worries you, you can always call the dr Monday. Remember they get paid good money to help you!!!
Good luck and Congrats!