8 week old sleeps a lot

Hi mummies! My baby girl is 8 weeks old today and I am wondering if she’s sleeping too much! Currently she wakes up every 3 hours to feed and is always very on time. She has at least 8 wet diapers and poops at least 2-3 times a day. However, she isn’t able to stay awake for long, often sleeps right after her feed. Many times she can’t even stay awake to burp, but will start fussing maybe 1 hour in to her nap due to reflux / gas. We hold her upright for at least 30-45 minutes even though she’s asleep. Is this normal? Do they still sleep so much at 8 weeks old? How do you squeeze in tummy time or activity time with barely any wake windows? Thank you!